Implement git-quiltimport

Implement git-quiltimport

Importing a quilt patch series into git is not very difficult
but parsing the patch descriptions and all of the other
minutia take a bit of effort to get right, so this automates it.

Since git and quilt complement each other it makes sense
to make it easy to go back and forth between the two.

If a patch is encountered that it cannot derive the author
from the user is asked.

Signed-off-by: Junio C Hamano <junkio@cox.net>