fix GC bug in compile_block, reported by Gwen

libgst:
2013-07-16  Paolo Bonzini  <bonzini@gnu.org>

	* libgst/comp.c: Do not call add_literal within an incubator context.
add assertion to add_literal to catch wrong use of the incubator

libgst:
2013-07-16  Paolo Bonzini  <bonzini@gnu.org>

	* libgst/oop.h: Add incubator depth.
	* libgst/oop.inl: Track incubator depth and add inc_current_depth().
	* libgst/comp.c: Assert that add_literal is not called within an
	incubator context (suggested by Gwen).
libgst: Fix a potential garbage collection problem in _gst_swap_objects

Protects the two oop args, otherwise one of them can be GC'ed if
they're tenured and not accessible from a Smalltalk context.

2013-07-09  Gwenael Casaccio <gwenael.casaccio@gmail.com>

	* oop.c: Protect oop1 and oop2 in _gst_swap_objects.