Use fast constructors if available

"slow" natives were removed in the mozjs commit:
http://hg.mozilla.org/mozilla-central/rev/66c8ad02543b

In order to work with both, add compatibility macros to compat.h,
and also update the ones in jsapi-util.h to use these.

Port all constructors to use these macros.

https://bugzilla.gnome.org/show_bug.cgi?id=632159