AC-130 Code

added a nice and simple mechanism to replicate C defines to GLSL

forgot to add the compat shader last commit, hehe (oops)

* added compatibility options: FSAA disabling (-noaa), compatibility compositing shader (-c) and terrain LOD tweaking (-t <value>, defaults to 40 and bound from below at 1)
* various little fixes and optimizations
* added level heightmap caching to speed up subsequent load times
* fixed false colouring of smoke sprites on Intel GPUs (buggy drivers, eh)
* work towards rendering entire prop map fields using a single draw call (current bottleneck; the target is to get the game running at interactive framerates on my Pentium M 1.5 GHz/Intel GMA 900 laptop)

Initial import from http://subversion.assembla.com/svn/iqpk/ac130 (r79)