Added usage for voxel rescale flag.
Ignore common image formats.
wlzerrno -> errNum for sanity.
Started to implement tiled values greyscan.
Fixed usage message.
Merge branch 'develop-bill' into develop-bill-tiledgreyscan
Many changes. Grey value scannning now works with tiled values tables. Code added to either work with tiled values tables or return an invalid values type error.
Change WlzEndGreyScan() so that its OK to call it even if the corresponding WlzInitGreyScan () wasnt called as long as the interval workspace was initialised to {0}.