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,
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<tr><td><span title='2020-06-24 19:55:22 +0100'>2020-06-24</span></td><td><a href='/guix/commit/nix/boost?id=cd43b55da7ab51c996a7a3449c78f2a493616106'>nix: Tweak .gitignore files.</a><span class='msg-avail'>...<span class='msg-tooltip'>Remove .gitignore entries where they match source files that are tracked in
Git.  This is relevant to me at least, as some code searching tools use
.gitignore files and will ignore matched files.
</span></span></td><td>Christopher Baines</td></tr>