Revision 1099843

- Git snapshot 20170428
  o Upstreams P2 and P3, also drop P1 and P4 which are Debian-specific
  o Fixes a crtical security vulnerability:
    https://ioquake3.org/2017/03/13/important-security-update-please-update-ioquake3-immediately/
- Build the game .so libraries, and put them in /usr/libexec/quake3
  o The .pk3 will now also be expected there, or in ~/.q3a as usual
- Now builds against SDL2 and Opus, removes Speex
- Cleanup build options, define meaningful version string