Log Message:
Near full rewrite of posix_headers:
- Implement a simple framework for automated header testing and generation
  using the c preprocessor.
- Make it installable on all platforms. On most platforms it will not install
  any files however.
- Bump revision to 0.5.

The changes should make it easier to add Interix support to this package.
Note that the package is still far from complete; for example the replacement
stdint.h does not yet provide fallback definitions for int_*t and friends
but relies on inttypes.h to provide them, which turns out to work for HPUX.