use LibRaw 0.16.0

LibRaw >= 1.15.0 no longer allows document_mode for grayscale
uninterpolated data, hence now directly reading raw data buffer.

QUESTIONS:
- does this produce different data than document_mode did?
- do need to set so many params for LibRaw if not calling
  libraw_dcraw_process() and libraw_dcraw_make_mem_image()?
record x-trans sensor's filter array

right now the only way to identify if the image is x-trans mosaiced is
to check for a dcraw-specific magic # 9 in filters

QUESTION:
- is there a better way to id non-bayer filter, such as a flag, or
  xtrans[0][0] == -1 means bayer?
demosaic x-trans initial try -- via linear interpolation

PROBLEMS/TODO:
- wrong at 1:1 view
- should use floats in interp. routine the whole way
- should use use x-trans interp. for all cases in process
- should use dcraw >= 9.19 demosaic algorithm
first pass at fast clip/zoom x-trans mosaiced image

quick copy of exisitng dt_iop_clip_and_zoom_demosaic_half_size,
presumably is wrong math, has buffer overflows, could be radically
improved, etc.
stub for x-trans in dt_image_flipped_filter

at least don't lose the x-trans magic '9' from dcraw
TODO: actually rotate the x-trans filter
allow debug builds
test code to print margins and test print pgm of incoming raw data
test print pgm of interpolate incoming

and lose some debugging code
lose some debugging code
bypass temperature module if x-trans mosaic data
working white balance for xtrans
use variable to recall image
less duplicate code, make special clause for x-trans
re-disable debug
lose debugging code from imageio.c
lose debugging code from pixel pipe
lose debugging code from demosaic
put roi back in for better or worse
lose premature optimization mms note
first pass at improvement of quick downsize