Teach rebase to rebase even if upstream is up to date

Normally, if the current branch is up to date, the rebase is aborted.
However, it may be desirable to allow rebasing even if the current
branch is up to date. When using the '--whitespace=fix' option -f is
implied.

Signed-off-by: Sverre Rabbelier <srabbelier@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -3,7 +3,7 @@
 # Copyright (c) 2005 Junio C Hamano.
 #
 
-USAGE='[--interactive | -i] [-v] [--onto <newbase>] [<upstream>|--root] [<branch>]'
+USAGE='[--interactive | -i] [-v] [--force-rebase | -f] [--onto <newbase>] [<upstream>|--root] [<branch>]'
 LONG_USAGE='git-rebase replaces <branch> with a new branch of the
 same name.  When the --onto option is provided the new branch starts
 out with a HEAD equal to <newbase>, otherwise it is equal to <upstream>
@@ -48,6 +48,7 @@ prec=4
 verbose=
 git_am_opt=
 rebase_root=
+force_rebase=
 
 continue_merge () {
 	test -n "$prev_head" || die "prev_head must be defined"
@@ -294,13 +295,21 @@ do
 		;;
 	--whitespace=*)
 		git_am_opt="$git_am_opt $1"
+		case "$1" in
+		--whitespace=fix|--whitespace=strip)
+			force_rebase=t
+			;;
+		esac
 		;;
 	-C*)
 		git_am_opt="$git_am_opt $1"
 		;;
 	--root)
 		rebase_root=t
 		;;
+	-f|--f|--fo|--for|--forc|force|--force-r|--force-re|--force-reb|--force-reba|--force_rebas|--force-rebase)
+		force_rebase=t
+		;;
 	-*)
 		usage
 		;;
@@ -419,10 +428,15 @@ if test "$upstream" = "$onto" && test "$mb" = "$onto" &&
 	# linear history?
 	! (git rev-list --parents "$onto".."$branch" | grep " .* ") > /dev/null
 then
-	# Lazily switch to the target branch if needed...
-	test -z "$switch_to" || git checkout "$switch_to"
-	echo >&2 "Current branch $branch_name is up to date."
-	exit 0
+	if test -z "$force_rebase"
+	then
+		# Lazily switch to the target branch if needed...
+		test -z "$switch_to" || git checkout "$switch_to"
+		echo >&2 "Current branch $branch_name is up to date."
+		exit 0
+	else
+		echo "Current branch $branch_name is up to date, rebase forced."
+	fi
 fi
 
 if test -n "$verbose"