From: Oleg Drokin <green@namesys.com>

This patch adds support for remounting taking into account all extra options
you may want to pass it.  (by Jeff Mahooney).

Also it reworks the parser to correctly deal with mutually exclusive options.
Now whatever option was specified last will take an effect.

- If you pass more than one jdev= option, the error will be reported and
  mount/remount refused.

- If you pass incorrect alloc= suboptions, the mount/remount will fail.
  (it did not before).

- nolargeio now actually looks at its argument.  Argument is expected to be
  numeric.  If it is zero, default io size is set to 128k (default setting),
  if it is non-zero, default io size is set to PAGE_SIZE.