reset: reject --no-(mixed|soft|hard|merge|keep) option

"git reset --no-mixed" behaved exactly like "git reset --mixed",
which was nonsense.

If there were only two kinds, e.g. "mixed" vs "separate", it might
have made sense to make "git reset --no-mixed" behave identically to
"git reset --separate" and vice-versa, but because we have many
types of reset, let's just forbid "--no-mixed" and negated form of
other types.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t7102-reset.sh b/t/t7102-reset.sh
index 22477f3..4287863 100755
--- a/t/t7102-reset.sh
+++ b/t/t7102-reset.sh
@@ -71,6 +71,16 @@
 	done | test_cmp .cat_expect -
 }
 
+# no negated form for various type of resets
+for opt in soft mixed hard merge keep
+do
+	test_expect_success "no 'git reset --no-$opt'" '
+		test_when_finished "rm -f err" &&
+		test_must_fail git reset --no-$opt 2>err &&
+		grep "error: unknown option .no-$opt." err
+	'
+done
+
 test_expect_success 'reset --hard message' '
 	hex=$(git log -1 --format="%h") &&
 	git reset --hard >.actual &&