The "tf" command that ships with Team Explorer Everywhere is pretty good, but
it is missing some functionality that we'd like. Most notably, there's no way
to get the content of files within a shelveset without unshelving it. That
means that in order to be able to post shelvesets, we need our own adapter.
This change is the beginnings of such an adapter, using the TFS SDK for Java.

Because we have such an adapter now, we can make it do exactly what we need for
interacting with TFS, which dramatically reduces the number of times it needs
to be called. This is good because each time it is called, we have to spin up
the whole JRE.

I've written this using a modular command format with individual commands for
each of the steps we have. These steps are:

- Verify the workspace and get the URL of the collection.
- Parse a given revision spec (with zero, one, or two "revisions" specified).
  This converts those revisions into either numeric changesets or special
  internal keys representing either the working copy or a shelveset.
- Do a diff based on the parsed revisions. Diffs are currently implemented for
  the working directory and shelvesets. I haven't yet implemented diffs for
  committed revisions, because that's somewhat more complex, but the existing
  tf.cmd-based implementation doesn't do it either.

This does not yet handle rbtools' -I and -X flags.

Testing done:
Used this to post pending and shelved changes.

Reviewed at https://reviews.reviewboard.org/r/8303/