Use multiple threads if available for softgpu.

VIVA OVERHEAD.  But it's actually generally faster this way, even with
only 2 cores running (but not a huge improvement then.)

On an i7, this improves things ~2.5x with 8 cores.
Optimize out some clear mode checks.

Since it's really common and the rasterizer is slow for large draws.
Merge pull request #4758 from unknownbrackets/softgpu2

Use multiple threads if available for softgpu.
Fix double free when saving.
As if softgpu wasn't slow enough already, implement bilinear filtering.
Allow held directional buttons to scroll up and down the list repeatedly.
Blackberry: Improve packaging.
Small tweaks to rel2 logging.
softgpu: Make texture lookups do less math.
softgpu: Avoid some ScreenToDrawing() overhead.
Move shared clut check to gstate.
Merge pull request #4766 from unknownbrackets/softgpu2

Improve softgpu performance a bit more
Return much more correct values for module info.

sceKernelQueryModuleInfo() was just completely wrong before.
Merge pull request #4762 from thedax/saveDialogAllowHeldBtns

Save/Load dialogs: Allow held directional buttons to scroll up and down the list repeatedly.
Merge pull request #4767 from unknownbrackets/moduleinfo

Return much more correct values for module info
Update MainScreen.cpp
Update native with libpng16 workaround for Mac
Readme update
SoftGPU: Quick and dirty lines and points implementation

No line/point texturing support yet.
isClutSharedForMipmaps: This was presumably inverted by accident?