Descender fix. ioMetrics.descent broken and always equal 0.

Descender usually and practically all the time negative. 

From freetype documentation:

descender -
The typographic descender of the face, expressed in font units. For font formats not having this information, it is set to ‘bbox.yMin’. Note that this field is usually negative. Only relevant for scalable formats.
Mac64 fixes, pixel format fix
Merge pull request #91 from codeservice/patch-2

Descender fix. ioMetrics.descent broken and always equal 0.
Missing float cast
Merge pull request #93 from codeservice/patch-3

Missing float cast
Rough fix for fringe alpha blending in the software renderer
Merge branch 'master' of github.com:haxenme/NME
Initial change to premultiplied alpha in GPU textures, will have to test more
Fixed tinting when using shaders, still need to figure it out without