Apply more thorough fixes while dealing with device opening and closing:

Apply more thorough fixes while dealing with device opening and closing:

- Determine open direction using 'flags', not 'mode'. This bug exist since
  past 4 years.
- Don't allow opening the same device twice, be it in a same or different
  direction.
- O_RDWR is allowed, provided that it is done by a single open (for example
  by mixer(8)) and the underlying hardware support true full-duplex operation.
- Do various paranoid checking in case other process/thread trying to hijack
  the same device twice (or more).

MFC after:	5 days