Replace mixed-case names such as gtkMenuMime with lowercase (gtk_menu_mime)
Replace FM_MODULE_REGISTER_xxx with fm_module_register_xxx for consistency.

Function names such as FM_MODULE_REGISTER_xxx don't look fine.
Replacing them have some side-effect - we cannot use "type" as module type
but I believe nobody will use such name ever.
Merge remote-tracking branch 'upstream'