format-patch: "rev1.." should mean "rev1..HEAD"

"rev1.." should mean "rev1..HEAD"; git-diff users are familiar
with that syntax.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-format-patch.sh

@@ -92,11 +92,18 @@ filelist=$tmp-files
 # 3. "rev1" "rev2	is equivalent to "rev1..rev2"
 #
 # We want to take a sequence of "rev1..rev2" in general.
+# Also, "rev1.." should mean "rev1..HEAD"; git-diff users are
+# familiar with that syntax.
 
 case "$#,$1" in
 1,?*..?*)
 	# single "rev1..rev2"
 	;;
+1,?*..)
+	# single "rev1.." should mean "rev1..HEAD"
+	set x "$1"HEAD"
+	shift
+	;;
 1,*)
 	# single rev1
 	set x "$1..HEAD"