Wrap ChamplainMemoryCache

	* champlain/champlainmm.h: Add memory-cache.h.
	* champlain/champlainmm/.gitignore: Ignore memory-cache.*.
	* champlain/src/champlain_signals.defs: Add ChamplainMemoryCache
	"size-limit" property.
	* champlain/src/filelist.am: Add memory-cache.hg.
	* champlain/src/memory-cache.[ccg|hg]: New files.
	* tools/extradefs/generate_extra_defs_libchamplain.cc: Add
	CHAMPLAIN_TYPE_MEMORY_CACHE.