Deb Packaging fixes: Build against Mozilla libs for Debian, conflict with "git"

Deb Packaging fixes: Build against Mozilla libs for Debian, conflict with "git"

This patch includes two fixes to the git-core Debian package:

    * Conflict with the GNU Interactive Tools package, which _also_
      wants to install /usr/bin/git.

    * Compile against the unencumbered Mozilla SHA1 code, instead of
      the iffy OpenSSL code, as much as possible.  This makes it easier to get
      the package included for distribution with Debian.

This has been based upon the original patch by Sebastian Kuzminsky
<seb@highlab.com>, but has been fixed up based upon feedback.

Signed-off-by: Ryan Anderson <ryan@michonline.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>