commit: more compact summary and without extra quotes

commit: more compact summary and without extra quotes

Update the report format again to save the screen real estates, while
avoiding from enclosing the one-line summary of the commit log inside
double quotes pair, which looks awkward when the message begins or ends
with a double quote.  The old format looked like this:

    [master]: created d9a5491: "foo:bar"

Simply removing the double quotes were found to be confusing as a message
often begins with a short-word (area of the system) and a colon.

The new format looks like this:

    [master d9a5491] foo:bar

As discussed in the git mailing list:

    http://thread.gmane.org/gmane.comp.version-control.git/101687/focus=101735

Signed-off-by: Santi Béjar <santi@agolina.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>