PNaCl updated, NaCl-* dropped, GCC 4.7, PartClass

- PNaCl updated to work with Pepper 31, NaCl-* dropped since GCC 4.4 hasn't been
  able to compile OpenZone for a long time
- legacy GCC hacks removed => GCC 4.7 required
- xstream -> xs
- client
  * PartSource, PartClass [not yet functional]