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=4df162962dc9ef45a4c716c4b462154249438718'>root</a>/<a href='/guix/log/tests?id=4df162962dc9ef45a4c716c4b462154249438718'>tests</a>/<a href='/guix/log/tests/git-authenticate.scm?id=4df162962dc9ef45a4c716c4b462154249438718'>git-authenticate.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/tests/git-authenticate.scm?id=4df162962dc9ef45a4c716c4b462154249438718&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-09-26 17:36:59 +0200'>2023-09-26</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=ba21eeb565fe414b3647173068a0f3eadd174c06'>tests: Assume ‘git’ is always available.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-02-14 11:23:08 +0100'>2022-02-14</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=ca87601dd97dd9d356409827802eb0f8a3a535f0'>git-authenticate: Ensure the target is a descendant of the introductory commit.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-02-14 11:23:07 +0100'>2022-02-14</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=36cb04df96623ffe8f1074172a4ed9e51bcf6e3a'>git-authenticate: Test introductory commit signature verification.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-12-22 10:53:19 +0100'>2021-12-22</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=9ebc9ca070a21ba0aeb3f61202a8071bb250ccc8'>tests: Move keys into ./tests/keys/ and add a third ed25519 key.</a><span class='msg-avail'>...</span></td><td>Attila Lendvai</td></tr>
<tr><td><span title='2020-06-28 23:26:53 +0200'>2020-06-28</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=0a8dd8aae5fad365c2f429d48e4085a3b3388332'>tests: Allow 'tests/git-authenticate.scm' to run when git/gpg is missing.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-06-20 13:18:11 +0200'>2020-06-20</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=7b06781a58326f251c4af6340379d68e3cb98adb'>tests: Skip tests that requires gpg when gpg is unavailable.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-06-16 16:10:46 +0200'>2020-06-16</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=1e2b9bf2d4ed4edc9ed70c51f414bb2890074a21'>tests: Move OpenPGP helpers to (guix tests gnupg).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-06-12 18:56:11 +0200'>2020-06-12</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=52c529ff20b389eb64ac033586e6b1a5c5d82cb5'>git-authenticate: Disallow SHA1 (and MD5) signatures.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-06-07 23:10:46 +0200'>2020-06-07</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=e78275608065ef073775fabb9f1a757da65851f2'>git-authenticate: Prevent removal of '.guix-authorizations'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-06-05 22:54:06 +0200'>2020-06-05</span></td><td><a href='/guix/commit/tests/git-authenticate.scm?id=c83eedba2361c3831d3efb5ad63d5077d636fb28'>git-authenticate: Add tests.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>