fix typo in find_mosaic.c

thanks dcb314

https://github.com/jcupitt/libvips/issues/81
fix some clang warnings
add SEQ operation hint to conv

conv operations can run sequentially over images
add clang notes
clang static analyze notes
small fixes for clang static analyzer

a few small things clang static analyzer found
sync
sync
Merge remote-tracking branch 'origin/master' into gate
now draws something