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) {
t> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=4089d7920fc5f27fefdde6b0fec17f3224e62377'>refs</a><a class='active' href='/guix/log/gnu/packages/pretty-print.scm'>log</a><a href='/guix/tree/gnu/packages/pretty-print.scm?id=4089d7920fc5f27fefdde6b0fec17f3224e62377'>tree</a><a href='/guix/commit/gnu/packages/pretty-print.scm?id=4089d7920fc5f27fefdde6b0fec17f3224e62377'>commit</a><a href='/guix/diff/gnu/packages/pretty-print.scm?id=4089d7920fc5f27fefdde6b0fec17f3224e62377'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/pretty-print.scm'>
<input type='hidden' name='id' value='4089d7920fc5f27fefdde6b0fec17f3224e62377'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=4089d7920fc5f27fefdde6b0fec17f3224e62377'>root</a>/<a href='/guix/log/gnu?id=4089d7920fc5f27fefdde6b0fec17f3224e62377'>gnu</a>/<a href='/guix/log/gnu/packages?id=4089d7920fc5f27fefdde6b0fec17f3224e62377'>packages</a>/<a href='/guix/log/gnu/packages/pretty-print.scm?id=4089d7920fc5f27fefdde6b0fec17f3224e62377'>pretty-print.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/pretty-print.scm?id=4089d7920fc5f27fefdde6b0fec17f3224e62377&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-06-30 21:13:51 +0300'>2020-06-30</span></td><td><a href='/guix/commit/gnu/packages/pretty-print.scm?id=13bd54b15da134012d40822c867bc70aa0bb14af'>gnu: Sort package modules alphabetically in (gnu packages pretty-print).</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>