git commit: Reformat output somewhat

git commit: Reformat output somewhat

Previously, we used to print something along the lines of

	Created commit abc9056 on master: Snib the sprock

but that output was sometimes confusing, as many projects use
the "subsystem: message" style of commit subjects (just like
this commit message does). When such improvements are done on
topic-branches, it's not uncommon to name the topic-branch the
same as the subsystem, leading to output like this:

	Created commit abc9056 on i386: i386: Snib the sprock

which doesn't look very nice and can be highly confusing.
This patch alters the format so that the noise-word "commit"
is dropped except when it makes the output read better and
the commit subject is put inside parentheses. We also
emphasize the detached case so that users do not overlook it
in case the commit subject is long enough to extend to the
next line. The end result looks thusly:

	normal case
	Created abc9056 (i386: Snib the sprock) on i386

	detached head
	Created DETACHED commit abc9056 (i386: Snib the sprock)

While we're at it, we rename "initial commit" to "root-commit"
to align it with the argument to 'git log', producing this:

	initial commit
	Created root-commit abc9056 (i386: Snib the sprock) on i386

Documentation/gittutorial-2.txt is updated accordingly so that
new users recognize what they're looking at.

Signed-off-by: Andreas Ericsson <ae@op5.se>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>