suppress external diff program when using git diff.
Merge pull request #967 from 0x20h/fix-git-diff

suppress external diff program when using git diff.
redis-cli: use keepalive socket option.

This should improve things in two ways:

1) Prevent timeouts caused by the execution of long commands.
2) Improve detection of real connection errors.

This is mostly effective only on Linux because of the bogus default
keepalive settings. In Linux we have OS-specific calls to set the
keepalive interval to reasonable values.
adding check error code

adding check error code
Cluster: REPLICATE subcommand and stub for clusterSetMaster().
SLAVEOF command refactored into a proper API.

We now have replicationSetMaster() and replicationUnsetMaster() that can
be called in other contexts (for instance Redis Cluster).
Cluster: actually setup replication in CLUSTER REPLICATE.
Make sure replicationSetMaster() works when ip argument is not an sds.
Cluster: fix maximum line length when loading config.

There are pathological cases where the line can be even longer a single
node may contain all the slots in importing/migrating state.
Cluster: don't perform startup slots sanity check for slaves.

If we are a cluster node the DB content will not match our configured
slots. Don't do the check at all.