More user guide
Split main function into Linux and OS X versions.

On OS X, running a program from the GUI adds random command line
arguments, which causes problems for flag.Parse().

This also allows Pond to run without POND=experimental in the
environment.
Some cleanups of the UI code.
Checkpoint of TPM NVRAM code.

This is before any of it is wired up.
TPM erasure storage support.

The client is now capable of using TPM NVRAM to safely erase old keys.