Add tracing for refreshTablet and action unlock.
Now using context everywhere for tm interactions.
Merge pull request #209 from youtube/trace

Add tracing for refreshTablet and action unlock.
Merge branch 'master' into replication
Merge pull request #214 from youtube/replication

Now using context everywhere for tm interactions.
Change VitessInputFormat key type

Make VitessInputFormat emit <NullWritable, RowWritable> instead of
<KeyspaceIdWritable, RowWritable>