added two input 3x3 texture sampling filter
two input 3x3 texture sampling filter now samples a 3x3 window for both textures
added approximate poisson image blending
fixed poisson equation bug
added comment about number of poisson iterations
Merge branch 'master' of https://github.com/iansimon/GPUImage

Conflicts:
	framework/GPUImage.xcodeproj/project.pbxproj
	framework/Source/GPUImage.h