Require the correct Yaml version for CMake as well.

The autotools configure script will complain if it can only find a 0.3.0 API version of yaml-cpp when the new 0.5.0 one is required. The CMake project however is happy, but the project then fails to compile.
Fuck compilers
ammo properties: bullet and explosion speed

bullet speed can now also be set on a per-ammo basis, and you can
customize the speed at which the animation plays.
Merge pull request #781 from JoakimSoderberg/cmake_yaml

Require the correct Yaml version for CMake as well.
explosion speed factor 10
xcom operatives: more efficient than we thought.
ammendment: not 20% per base

it's 20% chance to find one at all, and it'll be the first undiscovered one.