pefs status reports 6, 7

[Gleb Kurtsou]

It seems I've forgotten to submit status report last week.  Actually too
much has changed during this time, here is short list of changes (from
commit logs):
- Add support for multiply keys per filesystem
- Replace sbin/mount_pefs with sbin/pefs (it also installs link to
  /sbin/mount_pefs)
- Configuration utility is capable of mounting/unmounting filesystems,
  adding/deleting keys
- Add initial support for other cipher implementations (next candidate is
  skein, but most of stream ciphers based on hash function should fit)
- Use salsa20 for encryption
- Remove all cipher block alignment handling bloat
- Implement key generation function (using salsa20)
- Use uma zones for cryptographically sensitive info (to bzero memory
  before free)
- Add transparent mode. Emulate read-only filesystem if no keys specified
- Add key reference counting and locking
- Support nodes without keys

Next item on my todo list is fixing readdir and adding key chaining.