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

Fixes ValveSoftware/halflife#1558
- recoded mousethread and made it somewhat useful for very fast mouse
  movements (will reset CursorPos now) and thus also fixed some thread synchronization issues (hopefully)

Does not fix the following:
- IN_JoyMove doing nothing on Linux for Ricochet client
- Original mouse button down/up reacting when scoreboard mouse is on bugs.

Things to discuss:
- the IN_ResetMouse call [here in IN_GetDeltaMouse](https://github.com/ripieces/halflife/blob/3a819aa7dbd08caed54cd77f6779e5f8f4d07601/cl_dll/inputw32.cpp#L571): Is it okay to call it in every case or should it be called only when mx or my changed? Please note that [in IN_AcummulateMouse in the orginial code](https://github.com/ValveSoftware/halflife/blob/0a1528cfda0ef376e3e33c483191c6fac8599b7a/cl_dll/inputw32.cpp#L620) IN_ResetMouse is always called, so that would have to be made conditional too then, I guess.