refactor:1.global var with prefix g_
Merge branch 'master' of https://github.com/lingyi/twemcache

Conflicts:
	src/mc.c
	src/mc_ascii.c
	src/mc_assoc.c
	src/mc_connection.c
	src/mc_connection.h
	src/mc_core.c
	src/mc_core.h
	src/mc_items.c
	src/mc_klog.c
	src/mc_log.c
	src/mc_log.h
	src/mc_signal.c
	src/mc_slabs.c
	src/mc_stats.c
	src/mc_thread.c
	src/mc_thread.h
	src/mc_time.c