b=19689

b=19689
i=adilger
i=bobijam
i=nathan
o=Jim Garlick

Change tunefs.lustre and mkfs.lustre --mountfsoptions so that
exactly the specified mount options are used.
Leaving off any "mandatory" mount options is an error.
Leaving off any default mount options causes a warning, but is allowed.
Change errors=remount-ro from mandatory to default.
Sanitize the mount string before storing it.
Update man pages accordingly.

This hopefully makes two awkward situations less so:
- making errors=panic the default (before we had to append errors=remount-ro
  and hope ldiskfs parsing caused the last option to override the first)
- setting other mount options on the OST's dropped mballoc,extents
  without warning.