Modify bash completion to support help, version, and copyright.

"stg <tab>" lists all commands, including "help", "version", and
"copyright".

"stg he<tab>" completes "stg help "
"stg ver<tab>" completes "stg version "
"stg copy<tab>" completes "stg copyright "

"stg help <tab>" lists all commands /other than/ help, version, and
copyright.

"stg version <tab>" goes directly to shell completion.
"stg copyright <tab>" goes directly to shell completion.

Signed-off-by: Ted Pavlic <ted@tedpavlic.com>
Signed-off-by: Karl Hasselström <kha@treskal.com>