[PATCH] Do not create bogus branch from flag to git branch

If you run `git branch --help', you will unexpectedly have created a new
branch named "--help".  This simple patch adds logic and a usage
statement to catch this and similar problems, and adds a testcase for it.

Signed-off-by: Amos Waterland <apw@rossby.metr.ou.edu>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-branch.sh

@@ -2,6 +2,16 @@
 
 . git-sh-setup || die "Not a git archive"
 
+usage () {
+    echo >&2 "usage: $(basename $0)"' [<branchname> [start-point]]
+
+If no arguments, show available branches and mark current branch with a star.
+If one argument, create a new branch <branchname> based off of current HEAD.
+If two arguments, create a new branch <branchname> based off of <start-point>.
+'
+    exit 1
+}
+
 case "$#" in
 0)
 	headref=$(readlink "$GIT_DIR/HEAD" | sed -e 's|^refs/heads/||')
@@ -25,6 +35,12 @@ case "$#" in
 	head="$2^0" ;;
 esac
 branchname="$1"
+
+case "$branchname" in
+-*)
+	usage;;
+esac
+
 rev=$(git-rev-parse --verify "$head") || exit
 
 [ -e "$GIT_DIR/refs/heads/$branchname" ] && die "$branchname already exists"