Mouse code fixes

I tried to be extra careful, but this still needs review if the client DLLs (valve, dmc, ricochet) compile on Linux properly (they should).

Fixes ValveSoftware/halflife#1546
- fixed m_rawinput 1 mouse trapped inside a rectangle
- fixed thirdperson camera not working as it should

Does not fix the following:
- Original potential synchronisation issues with mouse thread in Half-Life
  client
- IN_JoyMove doing nothing on Linux for Ricochet client