Additional options for better reliability on faulty connections

Added options to clone, fetch, and quick-clone commands to help avoid/work around errors with faulty connections to TFS.  Also useful for working around issues with TFS servers exhibiting the KB981898 bug.

`clone`, `quick-clone`, and `fetch` commands:
`--verify-all` will verify that all files downloaded correctly, and will retry any failures with a get on the individual file.
`--verify-max-retries=N` will limit the maximum number of retries for failed validations.

`fetch` command only:
`--max-changesets=N` will limit the number of changesets fetched, reducing the upfront delay on fetches from TFS repositories with long histories.

The definition of a catch-22:
:rage: working over a crufty, unreliable VPN connection to overseas TFS
:smile: git-tfs
:confounded: cant initialize git-tfs because even an individual changeset get can blow up.