System info: also report enabled add-ons.

Based on idea & patch by @lijenstina over IRC (iirc :/ ).

release/scripts/modules/sys_info.py

@@ -212,4 +212,14 @@ def write_sysinfo(filepath):
         output.write(title("Cycles"))
         output.write(cycles.engine.system_info())
 
+    import addon_utils
+    addon_utils.modules()
+    output.write(title("Enabled add-ons"))
+    for addon in bpy.context.user_preferences.addons.keys():
+        addon_mod = addon_utils.addons_fake_modules.get(addon, None)
+        if addon_mod is None:
+            output.write("\t %s (MISSING)\n" % (addon))
+        else:
+            output.write("\t %s (%s, %s)\n" % (addon, addon_mod.bl_info.get('version', "UNKNOWN"), addon_mod.__file__))
+
     output.close()