Upgrade ctypes to dae9874cea870edf4d69dd6a2e51f554d23c7148

This is in anticipation of using new struct-stubs. Future commits
will use this. This commit deals with incompatabilities between
previous versions of ctypes.

* Some posix types were removed. Replaced these all with nativeint
  for now. Will revisit later to decide on what we want to do.
* Removed small cruft in Loop.ok