[p4] Bash completion with depot paths

[Andrew May]

I have been working on getting tab completions working for depot paths
with the bash completion file started by Frank Cusak. It took a bit of
flailing to get the dirs/files to expand ok without putting in the
extra spaces that would throw things off along the way.
That seemed to be the problem another person ran into on this mailing
list too.
I key off a "//" at first and then start running p4 dirs and p4 files
to find out what are the paths to complete.
I am not sure if it is the best way but I want to see if anyone else
had some ideas on it.

I would still like to add in jobspec/branch/client completion as well
depending on the command and options.

And the way it is now, "p4 ad<tab>" works, but "p4 -x ad<tab>" does not
work, since the function assumes the first arg is the command.

Frank has moved on from google and switched to zsh, so he isn't working
on the bash stuff any more.