mogstored_rack: add ability to change :io_size and :open_flags
mogstored_rack: add ability to change :io_size and :open_flags

This allows folks to try IO::SYNC, and maybe even IO::DIRECT.
Additionally, :io_size may be used to optimize IO::SYNC or
make IO::DIRECT _work_.

Removal of the "Tempfile" dependency means we no longer work
reliably on NFS, but nobody sane puts MogileFS devices on
NFS, anyways.  (Actually, nobody sane uses NFS if atomicity
is important :P)

drasch/mogilefs-client