Allow the configuration file and theme directory to be specified at run time.
Patch by Eelco Dolstra, from Nixpkgs.

--- slim-1.3.6/app.cpp	2013-10-02 00:38:05.000000000 +0200
+++ slim-1.3.6/app.cpp	2013-10-15 11:02:55.629263422 +0200
@@ -200,7 +200,9 @@
 
 	/* Read configuration and theme */
 	cfg = new Cfg;
-	cfg->readConf(CFGFILE);
+	char *cfgfile = getenv("SLIM_CFGFILE");
+	if (!cfgfile) cfgfile = CFGFILE;
+	cfg->readConf(cfgfile);
 	string themebase = "";
 	string themefile = "";
 	string themedir = "";
@@ -208,7 +210,9 @@
 	if (testing) {
 		themeName = testtheme;
 	} else {
-		themebase = string(THEMESDIR) + "/";
+		char *themesdir = getenv("SLIM_THEMESDIR");
+		if (!themesdir) themesdir = THEMESDIR;
+		themebase = string(themesdir) + "/";
 		themeName = cfg->getOption("current_theme");
 		string::size_type pos;
 		if ((pos = themeName.find(",")) != string::npos) {
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<div class='path'>path: <a href='/guix/log/?id=07bf68ed093bd66903c6c20b42caafe10688ea04'>root</a>/<a href='/guix/log/gnu?id=07bf68ed093bd66903c6c20b42caafe10688ea04'>gnu</a>/<a href='/guix/log/gnu/packages?id=07bf68ed093bd66903c6c20b42caafe10688ea04'>packages</a>/<a href='/guix/log/gnu/packages/gtk.scm?id=07bf68ed093bd66903c6c20b42caafe10688ea04'>gtk.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/gtk.scm?id=07bf68ed093bd66903c6c20b42caafe10688ea04&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2017-04-18 18:30:13 +0200'>2017-04-18</span></td><td><a href='/guix/commit/gnu/packages/gtk.scm?id=8c4b4b65624198261d6e583214da9aa7c5524290'>Merge branch 'master' into staging</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2017-04-17 21:25:17 -0400'>2017-04-17</span></td><td><a href='/guix/commit/gnu/packages/gtk.scm?id=40522a7e89bc169233ec724592c9439e8004f4ad'>gnu: gtk+: Update to 3.22.12.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/gtk.scm (gtk+): Update 3.22.12.
</span></span></td><td>Kei Kebreau</td></tr>
<tr><td><span title='2017-04-17 02:04:08 +0200'>2017-04-17</span></td><td><a href='/guix/commit/gnu/packages/gtk.scm?id=d1e4ad1b02b2ea888557d3272c50b676faf18ca4'>gnu: Fix typos in descriptions.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/admin.scm (di)[description]: Likewise.
* gnu/packages/bioinformatics.scm (r-annotate)[description]: Likewise.
* gnu/packages/datastructures.scm (sparsehash)[description]: Likewise.
* gnu/packages/dns.scm (knot)[description]: Likewise.
* gnu/packages/emacs.scm (emacs-idle-highlight)[synopsis, description]:
Likewise.
* gnu/packages/gnome.scm (libpeas)[description]: Likewise.
* gnu/packages/gtk.scm (python2-pygtk)[description]: Likewise.
* gnu/packages/kde-frameworks.scm (kactivities)[description]: Fix typo.
* gnu/packages/libevent.scm (perl-anyevent)[description]: Likewise.
* gnu/packages/machine-learning.scm (ghmm)[description]: Likewise.
* gnu/packages/mail.scm (mlmmj)[description]: Likewise.
* gnu/packages/maths.scm (vc)[description]: Likewise.
* gnu/packages/music.scm (gx-super-fuzz-lv2)[description]: Likewise.
* gnu/packages/networking.scm (nload)[description]: Likewise.
* gnu/packages/python.scm (python-execnet)[description]: Likewise.
* gnu/packages/terminals.scm (tilda)[description]: Likewise.
* gnu/packages/python.scm (python-execnet, python-tables)
(python2-coverage-test-runner, python2-rope)[description]: Likewise.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-04-15 21:10:27 -0400'>2017-04-15</span></td><td><a href='/guix/commit/gnu/packages/gtk.scm?id=61af2675d34a7387611623881f872fb0821ae1f5'>gnu: Add graphene.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/gtk.scm (graphene): New variable.
</span></span></td><td>Roel Janssen</td></tr>
<tr><td><span title='2017-04-15 20:56:22 -0400'>2017-04-15</span></td><td><a href='/guix/commit/gnu/packages/gtk.scm?id=2ff8deaeee5058372a518803b18e9b21a6ac67fc'>gnu: gdk-pixbuf: Update to 2.36.6.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/gtk.scm (gdk-pixbuf): Update to 2.36.6.
</span></span></td><td>Kei Kebreau</td></tr>
<tr><td><span title='2017-04-06 16:03:05 +0200'>2017-04-06</span></td><td><a href='/guix/commit/gnu/packages/gtk.scm?id=3433413b18f02436eb8459d097947257ac6973f7'>gnu: xorg-server@1.19.2: Update to 1.19.3.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is to adjust for the inputs and arguments change of xorg-server proper.

* gnu/packages/xorg.scm (xorg-server-1.19.2): Rename to ...
(xorg-server-1.19.3): ... this. Update version and origin.
* gnu/packages/gtk.scm (gtk+)[native-inputs]: Adjust accordingly.
[arguments]&lt;#:disallowed-references&gt;: Likewise.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2017-03-30 22:59:53 +0200'>2017-03-30</span></td><td><a href='/guix/commit/gnu/packages/gtk.scm?id=84157bb8bf2c610584e0836047da4c710f8eaf76'>Merge branch 'master' into core-updates</a><span class='msg-avail'>...<span class='msg-tooltip'>Most conflicts are from 6fd52309b8f52c9bb59fccffac53e029ce94b698.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2017-03-30 01:30:16 +0200'>2017-03-30</span></td><td><a href='/guix/commit/gnu/packages/gtk.scm?id=6fd52309b8f52c9bb59fccffac53e029ce94b698'>gnu: Use HTTPS for almost all gnu.org HOME-PAGEs.</a><span class='msg-avail'>...<span class='msg-tooltip'>All HTTP gnu.org (and supported subdomain) HOME-PAGEs changed to HTTPS.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>