Add my script for coping with git-svn and the need to rebase

changes for different branches. It's a bit rough right now,
but should be good enough for most people to try to use. It's
definitely 'tools' tree quality.

tools/tools/git/HOWTO

@@ -142,3 +142,18 @@ and 5, the commit hashes of all of your commits changed, including C1 and C2.
 You must go back and find the new commit hashes of your commits to pass to
 importgit.  Passing -r C1~..C2 would import your commits as they were *before*
 your code review fixes were applied.
+
+III. git-svn-rebase
+
+git-svn-rebase is a script that helps you keep current when using git 
+plus subversion as outline in https://wiki.freebsd.org/GitWorkflow/GitSvn
+since it's otherwise a pain to have many branhes active. It will rebase
+those branches that haven't been merged yet. Some tweaking may be needed
+if you have other, weird branches in your tree (including any stable
+branches). To run it just cd into the git subversion tree somewhere and
+type
+    $ git-svn-rebase
+and it will do its thing and leave the tree on the master branch.
+
+Your tree must be clean to start this, and while it tries to catch
+some failures, not all of them have been allowed for.

tools/tools/git/git-svn-rebase

@@ -0,0 +1,57 @@
+#!/bin/sh
+
+# $FreeBSD$
+
+# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+#
+#  Copyright (c) 2018 M. Warner Losh
+#
+#  Redistribution and use in source and binary forms, with or without
+#  modification, are permitted provided that the following conditions
+#  are met:
+#  1. Redistributions of source code must retain the above copyright
+#     notice, this list of conditions and the following disclaimer.
+#  2. Redistributions in binary form must reproduce the above copyright
+#     notice, this list of conditions and the following disclaimer in the
+#     documentation and/or other materials provided with the distribution.
+#
+#  THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+#  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+#  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+#  ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+#  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+#  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+#  OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+#  HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+#  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+#  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+#  SUCH DAMAGE.
+
+#
+# simple script to keep all my branches up to date while tracking
+# FreeBSD (or any upstream svn source) with git. Run it often, and it
+# will rebase all the branches so they don't get too stale.
+# Takes no args, and acts goofy if you have really old branches
+# which is why stable/* and mfc* are excluded. Caution to should be taken
+# when using this.
+#
+
+FAIL=
+echo ----------------- Checkout master for svn rebase ------------
+git checkout master
+echo ----------------- Rebasing our master to svn upstream  ------------
+git svn rebase
+for i in $(git branch --no-merge | grep -v stable/ | grep -v mfc); do
+	echo ----------------- Rebasing $i to the tip of master ------------
+	git rebase master $i || {
+	    echo "****************** REBASE OF $i FAILED, ABORTING *****************"
+	    FAIL="$FAIL $i"
+	    git rebase --abort
+	}
+done
+echo ----------------- Checkout out master again ------------
+git checkout master
+git branch
+if [ -n "$FAIL" ]; then
+    echo Failed branches: $FAIL
+fi