bash: Add space after unique command name is completed.

bash: Add space after unique command name is completed.

Because we use the nospace option for our completion function for
the main 'git' wrapper bash won't automatically add a space after a
unique completion has been made by the user.  This has been pointed
out in the past by Linus Torvalds as an undesired behavior.  I agree.

We have to use the nospace option to ensure path completion for
a command such as `git show` works properly, but that breaks the
common case of getting the space for a unique completion.  So now we
set IFS=$'\n' (linefeed) and add a trailing space to every possible
completion option.  This causes bash to insert the space when the
completion is unique.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>