add thresh.precondition to thinning Canny variant
add thresh.precondition to thinning Canny variant

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