Mounting a read-only md FS as read-only

[perryh at pluto.rain.com]

> does mount_ext2fs support readonly at all?

The manpage implies that it does:

  The options are as follows:

  -o      Options are specified with a -o flag followed by a comma sepa-
          rated string of options.  See the mount(8) man page for possible
          options and their meanings.