Support grayscale and other colorspaces in shade->usebackground case.
Support grayscale and other colorspaces in shade->usebackground case.

darcs-hash:20100623151536-f546f-ebf3223ed6ba6aecb8f4538d74efeadd87b016df.gz

nqv/mupdf,nqv/mupdf,nqv/mupdf,nqv/mupdf,nqv/mupdf,nqv/mupdf