Introduce git-checkout.sh

From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

Introduce a script to perform git checkout on an external git tree; use
git-checkout.sh in ioemu-dir-find.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson.citrix.com>

scripts/git-checkout.sh

@@ -0,0 +1,27 @@
+#!/bin/sh
+
+if test $# -lt 3; then
+	echo "Usage: $0 <tree> <tag> <dir>"
+	exit 1
+fi
+
+TREE=$1
+TAG=$2
+DIR=$3
+
+set -e
+
+if test \! -d $DIR-remote; then
+	rm -rf $DIR-remote $DIR-remote.tmp
+	mkdir $DIR-remote.tmp; rmdir $DIR-remote.tmp
+	$GIT clone $TREE $DIR-remote.tmp
+	if test "$TAG" ; then
+		cd $DIR-remote.tmp
+		$GIT branch -D dummy >/dev/null 2>&1 ||:
+		$GIT checkout -b dummy $TAG
+		cd ..
+	fi
+	mv $DIR-remote.tmp $DIR-remote
+fi
+rm -f $DIR
+ln -sf $DIR-remote $DIR