Add dtrace and systemtap support for gobject

This adds static markers and systemtap tapsets for:

* type creation
* object lifetimes (creation, ref, unref, dispose, finalize)
* signal creation and emission

Signal emissions and finalization marker have a corresponding
*_end (or *-end in dtrace) version that is when the corresponding
operation is finished.

https://bugzilla.gnome.org/show_bug.cgi?id=606044