optional enhancements:
- RPC use persistent client connection (configurable)
  add support for __enter__ and __exit__ for "with"
- NetBSD: call quota_open() only once during __init__
- FreeBSD >= 8.1: could use quotafile functions in -lutil
- support setting quota limits via RPC (v2)
- getmntent: distinguish end-of-list from error (when possible)?
- use tirpc even if SUN-RPC is implemented in libc too:
  requires linker options to control symbol resolution order
- automated unit-tests (as far as possible)
- automatically define NDEBUG for debug builds (if possible?)
- generate UNIX man page for dist
