This patch makes GTK+ look for additional modules in a list of directories
specified by the environment variable "GUIX_GTK3_PATH".  This can be used
instead of "GTK_PATH" to make GTK+ find modules that are incompatible with
other major versions of GTK+.

--- a/gtk/gtkmodules.c	2015-09-20 20:09:05.060590217 +0200
+++ b/gtk/gtkmodules.c	2015-09-20 20:10:33.423124833 +0200
@@ -52,6 +52,7 @@
 get_module_path (void)
 {
   const gchar *module_path_env;
+  const gchar *module_guix_gtk3_path_env;
   const gchar *exe_prefix;
   gchar *module_path;
   gchar *default_dir;
@@ -61,6 +62,7 @@
     return result;
 
   module_path_env = g_getenv ("GTK_PATH");
+  module_guix_gtk3_path_env = g_getenv ("GUIX_GTK3_PATH");
   exe_prefix = g_getenv ("GTK_EXE_PREFIX");
 
   if (exe_prefix)
@@ -68,7 +70,13 @@
   else
     default_dir = g_build_filename (_gtk_get_libdir (), "gtk-3.0", NULL);
 
-  if (module_path_env)
+  if (module_guix_gtk3_path_env && module_path_env)
+    module_path = g_build_path (G_SEARCHPATH_SEPARATOR_S,
+				module_guix_gtk3_path_env, module_path_env, default_dir, NULL);
+  else if (module_guix_gtk3_path_env)
+    module_path = g_build_path (G_SEARCHPATH_SEPARATOR_S,
+				module_guix_gtk3_path_env, default_dir, NULL);
+  else if (module_path_env)
     module_path = g_build_path (G_SEARCHPATH_SEPARATOR_S,
 				module_path_env, default_dir, NULL);
   else
9d4'>commit</a><a href='/guix/diff/tests/accounts.scm?id=5a1b2467361edcf8f2f9c7399658b4e136e979d4'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/accounts.scm'>
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<div class='path'>path: <a href='/guix/log/?id=5a1b2467361edcf8f2f9c7399658b4e136e979d4'>root</a>/<a href='/guix/log/tests?id=5a1b2467361edcf8f2f9c7399658b4e136e979d4'>tests</a>/<a href='/guix/log/tests/accounts.scm?id=5a1b2467361edcf8f2f9c7399658b4e136e979d4'>accounts.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/accounts.scm?id=5a1b2467361edcf8f2f9c7399658b4e136e979d4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-08-28 00:27:14 +0200'>2019-08-28</span></td><td><a href='/guix/commit/tests/accounts.scm?id=dd4e46edda6c255ca170a6650c6f92b16ff50a3f'>accounts: Delete duplicate entries.</a><span class='msg-avail'>...<span class='msg-tooltip'>When adding multiple instances of a service requiring some user
account/group, we could end up with multiple entries for that account or
group in /etc/passwd or /etc/group.

* gnu/build/accounts.scm (database-writer)[write-entries]: Add call to
'delete-duplicates'.
* tests/accounts.scm ("write-passwd with duplicate entry"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-04-27 16:30:40 +0200'>2019-04-27</span></td><td><a href='/guix/commit/tests/accounts.scm?id=0c329bf4b0c00abdc9a7d9c818d36d4d60b3005d'>tests: Adjust accounts test to shell-as-config change.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to 504a0fc636ec591e65b4a229a37e522e425d8a0c.

* tests/accounts.scm ("allocate-passwd with previous state"): Change
expected 'shell' for "alice" to "/bin/sh".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-25 23:37:06 +0100'>2019-03-25</span></td><td><a href='/guix/commit/tests/accounts.scm?id=cf848cc0a17a3a58d600116896f6e7abfb0440d4'>accounts: Add default value for the 'home-directory' field of &lt;user-account&gt;.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/accounts.scm (&lt;user-account&gt;)[home-directory]: Mark as
thunked and add a default value.
(default-home-directory): New procedure.
* doc/guix.texi (User Accounts): Remove 'home-directory' from example.
* gnu/system/examples/bare-bones.tmpl: Likewise.
* gnu/system/examples/beaglebone-black.tmpl: Likewise.
* gnu/system/examples/desktop.tmpl: Likewise.
* gnu/system/examples/docker-image.tmpl: Likewise.
* gnu/system/examples/lightweight-desktop.tmpl: Likewise.
* gnu/system/install.scm (installation-os): Likewise.
* gnu/tests.scm (%simple-os): Likewise.
* gnu/tests/install.scm (%minimal-os, %minimal-os-on-vda):
(%separate-home-os, %encrypted-root-os, %btrfs-root-os): Likewise.
* tests/accounts.scm ("allocate-passwd")
("allocate-passwd with previous state"): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-07 20:05:09 +0100'>2019-03-07</span></td><td><a href='/guix/commit/tests/accounts.scm?id=ec600e4544729f1aaf46fa5162bba334515d0de5'>Add (gnu build accounts).</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/accounts.scm, tests/accounts.scm: New files.
* Makefile.am (SCM_TESTS): Add tests/accounts.scm.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add build/accounts.scm.
</span></span></td><td>Ludovic Courtès</td></tr>