Write a "checkhealth" script to run under vsh

[mmalcomson]

Since vsh has all sorts of tie-ins with other programs, the users environment can easily cause troubles.

It would be nice to provide a small introduction tutorial and script to check what might be wrong.

• Is TERM set to dumb?
• Do we have possible-completions bound in readline?
• If so, has vsh_completions_cmd correctly identified the relevant keys.
• Ensure pagination is turned off in gdb (based on TERM).
• Recommend that stty is handled so that can map C-q.
• TODO -- anything else?

Then have an introduction file: Existing .vsh file to show some features that the user can step through. ix, ic, <F3>, etc commands.

[mmalcomson]

Since zsh resets some tty variables on each new prompt, it seems like it would be good to check that and mention it. (I personally have if TERM=dumb exec bash in my zshrc so that machines running zsh don't act wierd when I ssh into them).