[PATCH] Extend "git reset" to take a reset point

[PATCH] Extend "git reset" to take a reset point

This was triggered by a query by Sam Ravnborg, and extends "git reset" to
reset the index and the .git/HEAD pointer to an arbitrarily named point.

For example

	git reset HEAD^

will just reset the current HEAD to its own parent - leaving the working
directory untouched, but effectively un-doing the top-most commit. You
might want to do this if you realize after you committed that you made a
mistake that you want to fix up: reset your HEAD back to its previous
state, fix up the working directory and re-do the commit.

If you want to totally un-do the commit (and reset your working directory
to that point too), you'd first use "git reset HEAD^" to reset to the
parent, and then do a "git checkout -f" to reset the working directory
state to that point in time too.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>