Create background context for agent in main().
Move reparent agent actions to a separate file.

Also apply Golint suggestions.
Fix function that was renamed for Golint.
Use SplitHostPort to handle hosts with colons.
Use JoinHostPort to handle hosts with colons.
Avoid divide-by-zero and fix units in cgzip_test.
Document the meaning of the context passed into NewActionAgent.
Merge pull request #273 from youtube/cgzip_test

Avoid divide-by-zero and fix units in cgzip_test.
Merge pull request #272 from youtube/split-host-port

Handle hosts with colons (IPv6)
Merge pull request #267 from youtube/fast-external-reparent

Cleaning up tabletmanager RPCAgent.
Merge branch 'master' into replication