PSYNC2 fix - promoted slave should hold on to it's backlog
PSYNC2 fix - promoted slave should hold on to it's backlog

after a slave is promoted (assuming it has no slaves
and it booted over an hour ago), it will lose it's replication
backlog at the next replication cron, rather than waiting for slaves
to connect to it.
so on a simple master/slave faiover, if the new slave doesn't connect
immediately, it may be too later and PSYNC2 will fail.

pmem/redis,neomantra/redis,ctripcorp/redis,spinlock/redis,PKRoma/redis,spinlock/redis,nnog/redis,ctripcorp/redis,ofirluzon/redis,PKRoma/redis,pmem/redis,ofirluzon/redis,charsyam/redis,antirez/redis,rogerchina/redis,charsyam/redis,neomantra/redis,soloestoy/redis,ofirluzon/redis,soloestoy/redis,nnog/redis,PKRoma/redis,yossigo/redis,yossigo/redis,PKRoma/redis,rogerchina/redis,soveran/redis,soloestoy/redis,GitHubMota/redis,soveran/redis,soveran/redis,oranagra/redis,pmem/redis,ctripcorp/redis,soloestoy/redis,nnog/redis,GitHubMota/redis,soveran/redis,charsyam/redis,spinlock/redis,rogerchina/redis,rogerchina/redis,neomantra/redis,oranagra/redis,neomantra/redis,soloestoy/redis,antirez/redis,PKRoma/redis,spinlock/redis,charsyam/redis,ctripcorp/redis,oranagra/redis,antirez/redis,neomantra/redis,nnog/redis,oranagra/redis,ofirluzon/redis,GitHubMota/redis,charsyam/redis,yossigo/redis,oranagra/redis,pmem/redis,antirez/redis,yossigo/redis,ofirluzon/redis,yossigo/redis,GitHubMota/redis