Make FindAllTabletAliasesInShard better.

It now uses the new replication graph.
Fix InitTablet to write master to shard.
Re-working ShardExternallyReparented.

So it works with Shard having the master record.
Moving a function.
Merge branch 'master' into replication
Not changing a shard master during rebuilds now.
Make external reparent more robust.
Merge branch 'master' into replication
Adding comment.
Now Reparenting actions use new replication graph.
Removing a few obsolete methods and code.
Merge branch 'master' into replication
Use better suffixes for new stats vars.
Handling EINTR in gorpc.dial()
Merge branch 'master' of github.com:youtube/vitess
Rename Cache related vars more consistently.
stats tx -> transaction
Fix tests for tx pool.
Mild improvement in GetSessionId check.
Merge branch 'vars-rename'