Add grayscale closing tests.
Add grayscale closing tests.

cha007/vigra,ThomasWalter/vigra,cbecker/vigra,DaveRichmond-/vigra,mmuellner/vigra,timoMa/vigra,timoMa/vigra,dstoe/vigra,kod3r/vigra,hmeine/vigra,capturePointer/vigra,capturePointer/vigra,psteinb/vigra,capturePointer/vigra,timoMa/vigra,stuarteberg/vigra,capturePointer/vigra,psteinb/vigra,cbecker/vigra,martinsch/vigra,dstoe/vigra,timoMa/vigra,martinsch/vigra,timoMa/vigra,cha007/vigra,funkey/vigra,mmuellner/vigra,funkey/vigra,timoMa/vigra,dagophil/vigra,hmeine/vigra,dstoe/vigra,kod3r/vigra,funkey/vigra,timoMa/vigra,psteinb/vigra,kod3r/vigra,dstoe/vigra,mmuellner/vigra,martinsch/vigra,xiwei-zhang/vigra,stuarteberg/vigra,capturePointer/vigra,hmeine/vigra,hmeine/vigra,hmeine/vigra,kod3r/vigra,stuarteberg/vigra,xiwei-zhang/vigra,DaveRichmond-/vigra,funkey/vigra,dagophil/vigra,dagophil/vigra,DaveRichmond-/vigra,martinsch/vigra,dagophil/vigra,xiwei-zhang/vigra,psteinb/vigra,xiwei-zhang/vigra,dagophil/vigra,psteinb/vigra,DaveRichmond-/vigra,cha007/vigra,dagophil/vigra,xiwei-zhang/vigra,cbecker/vigra,stuarteberg/vigra,ThomasWalter/vigra,martinsch/vigra,capturePointer/vigra,psteinb/vigra,mmuellner/vigra,kod3r/vigra,kod3r/vigra,stuarteberg/vigra,ThomasWalter/vigra,funkey/vigra,mmuellner/vigra,ThomasWalter/vigra,cha007/vigra,xiwei-zhang/vigra,ThomasWalter/vigra,kod3r/vigra,cbecker/vigra,DaveRichmond-/vigra,cbecker/vigra,xiwei-zhang/vigra,ThomasWalter/vigra,cbecker/vigra,martinsch/vigra,dstoe/vigra,stuarteberg/vigra,ThomasWalter/vigra,DaveRichmond-/vigra,dagophil/vigra,cha007/vigra,cha007/vigra,capturePointer/vigra,dstoe/vigra,stuarteberg/vigra,dstoe/vigra,hmeine/vigra,funkey/vigra,mmuellner/vigra,cha007/vigra,funkey/vigra,psteinb/vigra,mmuellner/vigra,hmeine/vigra,DaveRichmond-/vigra