bugfix: replace lastcmd with cmd when rewrite BRPOPLPUSH as RPOPLPUSH
bugfix: replace lastcmd with cmd when rewrite BRPOPLPUSH as RPOPLPUSH

There are two problems if we use lastcmd:

1. BRPOPLPUSH cannot be rewrited as RPOPLPUSH in multi/exec
    In mulit/exec context, the lastcmd is exec.
2. Redis will crash when execute RPOPLPUSH loading from AOF
    In fakeClient, the lastcmd is NULL.

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