Support the PURPLE_PLUGIN_PATH environment variable.  This patch is based on
one from Nixpkgs, but properly handles the case where that variable is unset.

--- pidgin-2.10.11/libpurple/plugin.c.orig	2014-11-23 11:41:25.000000000 -0500
+++ pidgin-2.10.11/libpurple/plugin.c	2015-08-04 14:31:02.257366144 -0400
@@ -1178,8 +1178,19 @@
 void
 purple_plugins_init(void) {
 	void *handle = purple_plugins_get_handle();
+	const gchar *purple_plugin_path;
 
 	purple_plugins_add_search_path(LIBDIR);
+	purple_plugin_path = g_getenv("PURPLE_PLUGIN_PATH");
+	if (purple_plugin_path && *purple_plugin_path) {
+		gchar **paths = g_strsplit(purple_plugin_path, ":", -1);
+		if (paths) {
+			gchar **p;
+			for (p = paths; *p; ++p)
+				if (**p) purple_plugins_add_search_path(*p);
+		}
+		g_strfreev(paths);
+	}
 
 	purple_signal_register(handle, "plugin-load",
 						 purple_marshal_VOID__POINTER,
witch'/></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=1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4'>refs</a><a class='active' href='/guix/log/gnu/packages/mastodon.scm'>log</a><a href='/guix/tree/gnu/packages/mastodon.scm?id=1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4'>tree</a><a href='/guix/commit/gnu/packages/mastodon.scm?id=1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4'>commit</a><a href='/guix/diff/gnu/packages/mastodon.scm?id=1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/mastodon.scm'>
<input type='hidden' name='id' value='1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4'/><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=1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4'>root</a>/<a href='/guix/log/gnu?id=1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4'>gnu</a>/<a href='/guix/log/gnu/packages?id=1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4'>packages</a>/<a href='/guix/log/gnu/packages/mastodon.scm?id=1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4'>mastodon.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/mastodon.scm?id=1231ce9a0735f3ebb6456de97dc96a5cabcc9ca4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-07-27 13:11:37 +0300'>2020-07-27</span></td><td><a href='/guix/commit/gnu/packages/mastodon.scm?id=069da2433e429a6b9b2a0d2a4bea40418d465c4d'>gnu: Add python-mastodon-py.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2020-06-30 09:45:44 +0300'>2020-06-30</span></td><td><a href='/guix/commit/gnu/packages/mastodon.scm?id=a9ff5b72a69a9d97a0f0ae59f24956df0600ef3f'>gnu: toot: Update to 0.27.0.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2020-04-16 22:40:39 +0300'>2020-04-16</span></td><td><a href='/guix/commit/gnu/packages/mastodon.scm?id=e40e7fdf0971feaecd622e927a92929c7b03d681'>gnu: toot: Update to 0.26.0.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2020-04-01 10:22:33 +0300'>2020-04-01</span></td><td><a href='/guix/commit/gnu/packages/mastodon.scm?id=fba0fea4a68ae5905a0fdb10f0ec8134fb65d58f'>gnu: toot: Adjust custom phases.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2020-04-01 10:21:48 +0300'>2020-04-01</span></td><td><a href='/guix/commit/gnu/packages/mastodon.scm?id=b7417f3d54346981c9fd6b3985cdfbca7e167ffb'>gnu: toot: Update to 0.25.2.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>