GTM HA for 0.9.7

Committed the patch.   Now GTM's transaction backup to the standby is accurate, even in heavy workload.   Remaining issues are:

1. tcp_keepalives feature works to monitor client connection at the server.   Need some more work to enable monitoring server connection at clients.
2. Need to add "status" feature.   I once considered to add this to gtm_ctl.   It may work but new command can be okay too.    Anyway, this feature should be implemented using normal communication with gtm/gtm_proxy, not signal.
3. "gtminit", associated with XC cluster bootstrap.