gallium: fix additional glCopyTex[Sub]Image issues
gallium: fix additional glCopyTex[Sub]Image issues

Use the TexFormat->StoreImage() routine for fallbacks.  This handles the
case of copying RGBA framebuffer data into an RGBA texture when the base
format is GL_RGB (or GL_LUMINANCE, etc).  In that case, we need to set
the texture's alpha=1 and override the framebuffer's alpha.

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