Add git-resquash.sh to repository

This differs from my old git-resquash.sh in that it uses the newer
`git rebase --keep-base` if available

scripts/git/git-install-tools.sh

@@ -3,7 +3,7 @@
 SCRIPT_NAME=$(basename "$0")
 SCRIPTS_DIR=$(dirname "$0")
 
-TOOL_NAMES=(push-all pull-all merge-forward list-tor-branches)
+TOOL_NAMES=(push-all pull-all merge-forward list-tor-branches resquash)
 
 function usage()
 {

scripts/git/git-resquash.sh

@@ -0,0 +1,46 @@
+#!/bin/sh
+#
+# Provides a convenient alias for "git rebase -i --autosquash --keep-root"
+# on gits that have it, and a replacement on gits that don't.
+
+set -e
+
+PARENT="$1"
+
+if test "x$PARENT" = "x"; then
+    echo "You must specify the parent branch."
+    exit 1
+fi
+
+# Can we use git rebase --keep-base?  Detect the git version to find out.
+GITVER=$(git version)
+if test "$(echo "$GITVER"|cut -d ' ' -f 1-2)" = "git version"; then
+    # --keep-base was added in git 2.24.  Detect if we have that version.
+    GITVER=$(echo "$GITVER" | cut -d ' ' -f 3)
+    major=$(echo "$GITVER" | cut -d . -f 1)
+    minor=$(echo "$GITVER" | cut -d . -f 2)
+    if test "$major" -lt 2; then
+        USE_KEEP_BASE=0
+    elif test "$major" -eq 2 && test "$minor" -lt 24; then
+        USE_KEEP_BASE=0
+    else
+        USE_KEEP_BASE=1
+    fi
+else
+    # This isn't a git that reports its version in a way recognize; assume that
+    # --keep-base will work
+    USE_KEEP_BASE=1
+fi
+
+if test "x$USE_KEEP_BASE" = "x1" ; then
+    exec git rebase -i --autosquash --keep-base "${PARENT}"
+else
+    REV=$(git log --reverse --format='%H' "${PARENT}..HEAD" | head -1)
+
+    if test "x${REV}" = "x"; then
+        echo "No changes here since ${PARENT}"
+        exit 1
+    fi
+
+    exec git rebase -i --autosquash "${REV}^"
+fi