* cppfiles.c (_cpp_pop_file_buffer): Change return type to bool
	and return true if _cpp_push_next_buffer pushed a new include
	file.
	* cpplib.c (_cpp_pop_buffer): Only call obstack_free if
	_cpp_pop_file_buffer did not push a new file.
	* cpphash.h (_cpp_pop_file_buffer): Update declaration.

From-SVN: r48507