Normalize ACL's.

Added munging of ACL's into the canonical format.  The format from
setfacl was used as a guide. With the exception that the type
field can not be left out (defaults to user in setfacl).

In general I tried to be strict.  Here are some notes.
- The type must be either the inital letter or the full type, nothing
  else is accepted.
- The "who" field is not verified in any way.
- The permssions field may only contain one of each 'r', 'w' and 'x'
  however the order is not checked.  The only other character it can
  contain is '-' which is ignored. An octal digit is also accepted in
  which case it must be the only character.
Merge pull request #5 from kevincox/normalize

Normalize ACL's.