[gtk+] Add support for loading gtk3-only modules

[Lars Uebernickel <larsu src gnome org>]

commit 3e81653bd320b9d5c760c2731a225f546f353c7a
Author: Lars Uebernickel <lars uebernickel canonical com>
Date:   Tue Feb 3 11:01:29 2015 +0100

    Add support for loading gtk3-only modules
    
    Introduce GTK3_MODULES environment variable for modules that don't work
    in gtk3. The list of modules is now $GTK3_MODULES:$GTK_MODULES.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=743917

 docs/reference/gtk/running.sgml |   14 ++++++++++++--
 gtk/gtkmain.c                   |   13 ++++++++++++-
 2 files changed, 24 insertions(+), 3 deletions(-)
---
diff --git a/docs/reference/gtk/running.sgml b/docs/reference/gtk/running.sgml
index 1c406a3..a826dca 100644
--- a/docs/reference/gtk/running.sgml
+++ b/docs/reference/gtk/running.sgml
@@ -36,7 +36,7 @@ some additional commandline options.
 
 <para>
 A list of modules to load in addition to those specified in the
-<envar>GTK_MODULES</envar> environment variable and the
+<envar>GTK3_MODULES</envar> environment variable and the
 <literal>gtk-modules</literal> setting.
 </para>
 </formalpara>
@@ -223,14 +223,24 @@ additional environment variables.
 </formalpara>
 
 <formalpara>
-  <title><envar>GTK_MODULES</envar></title>
+  <title><envar>GTK3_MODULES</envar></title>
 
   <para>
     A list of modules to load. Note that GTK+ also allows to specify modules to load via a commandline 
option (<option>--gtk-module</option>) and with the <literal>gtk-modules</literal> setting.
   </para>
+</formalpara>
+
+<formalpara>
+  <title><envar>GTK_MODULES</envar></title>
+
+  <para>
+    A list of modules to load in addition to the ones in the <envar>GTK3_MODULES</envar> variable.
+  </para>
   <warning>
     Note that this environment variable is read by GTK+ 2.x too,
     which may not have the same set of modules available for loading.
+    Use <envar>GTK3_MODULES</envar> for modules that are only compatible
+    with GTK+ 3.
   </warning>
 </formalpara>
 
diff --git a/gtk/gtkmain.c b/gtk/gtkmain.c
index 88e3260..36c2586 100644
--- a/gtk/gtkmain.c
+++ b/gtk/gtkmain.c
@@ -657,9 +657,20 @@ do_pre_parse_initialization (int    *argc,
     }
 #endif  /* G_ENABLE_DEBUG */
 
-  env_string = g_getenv ("GTK_MODULES");
+  env_string = g_getenv ("GTK3_MODULES");
   if (env_string)
     gtk_modules_string = g_string_new (env_string);
+
+  env_string = g_getenv ("GTK_MODULES");
+  if (env_string)
+    {
+      if (gtk_modules_string)
+        g_string_append_c (gtk_modules_string, G_SEARCHPATH_SEPARATOR);
+      else
+        gtk_modules_string = g_string_new (NULL);
+
+      g_string_append (gtk_modules_string, env_string);
+    }
 }
 
 static void