mesa: adjust glBitmap coords by a small epsilon
mesa: adjust glBitmap coords by a small epsilon

Fixes problem with bitmaps jumping around by one pixel depending on window
size.  The rasterpos is often X.9999 instead of X+1.
Run progs/redbook/drawf and resize window to check.

Cherry picked from gallium-0.1 branch

tokyovigilante/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,benaadams/glsl-optimizer,metora/MesaGLSLCompiler,KTXSoftware/glsl2agal,dellis1972/glsl-optimizer,zz85/glsl-optimizer,adobe/glsl2agal,wolf96/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,djreep81/glsl-optimizer,mcanthony/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,bkaradzic/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,metora/MesaGLSLCompiler,zz85/glsl-optimizer,mapbox/glsl-optimizer,benaadams/glsl-optimizer,benaadams/glsl-optimizer,bkaradzic/glsl-optimizer,KTXSoftware/glsl2agal,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,KTXSoftware/glsl2agal,mapbox/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,mapbox/glsl-optimizer,wolf96/glsl-optimizer,mapbox/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,bkaradzic/glsl-optimizer,jbarczak/glsl-optimizer,adobe/glsl2agal,benaadams/glsl-optimizer,zz85/glsl-optimizer,wolf96/glsl-optimizer,zeux/glsl-optimizer,adobe/glsl2agal,tokyovigilante/glsl-optimizer,bkaradzic/glsl-optimizer,mapbox/glsl-optimizer,adobe/glsl2agal,wolf96/glsl-optimizer,djreep81/glsl-optimizer,KTXSoftware/glsl2agal,zz85/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,KTXSoftware/glsl2agal,zeux/glsl-optimizer,adobe/glsl2agal,dellis1972/glsl-optimizer,jbarczak/glsl-optimizer,zeux/glsl-optimizer,jbarczak/glsl-optimizer,mcanthony/glsl-optimizer,dellis1972/glsl-optimizer,metora/MesaGLSLCompiler,dellis1972/glsl-optimizer,djreep81/glsl-optimizer