fix a warning on OS X (defined but unused)
fix another warning on OS X:

gint64 is long int here, not long long int like int64_t
Histogram: replace dt_iop_roi_t with new dt_histogram_roi_t
Spots IOP: legacy_params(): adapt for latest mask changes
dt_masks_legacy_params(): refactor v1 -> v2 to a function, prepare for v3
Needed preparations for loading of uncropped, unscaled (B/W) raw images
dt_imageio_open_rawspeed(): better levels handling
Fixes DNGs from ML cr2hdr.

Thanks to <rwh> and <hal9k_> for making me notice it.
rawprepare: new IOP, no-op (passthrough)
rawprepare: allow tiling

FIXME: verify this!
dt_imageio_open_rawspeed(): break everything! Stop scaling (B/W).
dt_imageio_open_rawspeed_sraw(): break everything! Stop scaling (B/W).
rawprepare: scaling for raw mosaic buffers
rawprepare: scaling for floating point buffers
Deflicker (histogram of: source raw data): fix (no scaling)
dt_dev_pixelpipe_disable_{after,before}(): do not disable matching-one IOPs

pre:iopname now means: do not process any iops after iopname iop, and give us data after iopname iop
post:iopname now means: do not process any iops before iopname iop, start processing with first iop - iopname iop
Create HDR: adapt to scaling
rawprepare: prepare for using blackLevelSeparate
rawprepare: raw mosaic: sepBlack
Rawprepare IOP: GUI
rawprepare: scaling for raw mosaic buffers [SSE]