Provide more meaningful output from 'git init-db'.

Back in the old days of Git when people messed around with their
GIT_DIR environment variable more often it was nice to know whether
or not git-init-db created a .git directory or used GIT_DIR.
As most users at that time were rather technical UNIXy folk the
message "defaulting to local storage area" made sense to some and
seemed reasonable.

But it doesn't really convey any meaning to the new Git user,
as they don't know what a 'local storage area is' nor do they
know enough about Git to care.  It also really doesn't tell the
experienced Git user a whole lot about the command they just ran,
especially if they might be reinitializing an existing repository
(e.g. to update hooks).

So now we print out what we did ("Initialized empty" or
"Reinitialized existing"), what type of repository ("" or "shared"),
and what location the repository will be in ("$GIT_DIR").

Suggested in part by Andy Parkins in his Git 'niggles' list
(<200612132237.10051.andyparkins@gmail.com>).

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

Documentation/core-tutorial.txt

@@ -57,7 +57,7 @@ $ git-init-db
 to which git will reply
 
 ----------------
-defaulting to local storage area
+Initialized empty Git repository in .git/
 ----------------
 
 which is just git's way of saying that you haven't been doing anything