Revamp bash_completion.

Revamp bash_completion.

This rewrite of the bash_completion script improves completion for the
para_client and para_audioc commands significantly.

One flaw which is fixed by this patch is related to the fact that by default
readline creates COMP_WORDS by splitting at characters that separate a shell
command, including "=", but for paraslash commands we only want to split at
spaces. So we modify the completer to return the special code 124 to instruct
readline to try split again with space as the only delimiter.