nvfx: draw: make perspective corrective texturing work
nvfx: draw: make perspective corrective texturing work

We must divide everything in the position by w, and emit position as
a 4-component vector.

Not sure why we must divide, but it works (see progs/redbook/checker).

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