gcc has optimizations for include guards that only work if they are outermost in the the header. https://bugzilla.gnome.org/show_bug.cgi?id=689810
Move internal accel map API there and update all users. Also, add an internal function to create an accel path for an action and parameter, and use it in gtkapplication.c and gtkmodelmenuitem.c instead of duplicating that code.