This patch ports some varobj cleanups from Apple's version, in preparation
for some much more interesting ports. OK?	

- Volodya

	Port from Apple's version.
	gdb/
	* varobj.c (type_changeable): Rename to...
	(varobj_value_is_changeable_p): ...this. Adjust all callers.
	(is_root_p): New function. Use it everywhere.