Just use the image format as-is. The only problem now is that we don't
support all formats for loading in file-raw yet.

(cherry picked from commit 01e0675f)

 Conflicts:
	plug-ins/common/file-raw-data.c

We only set tiff_mode for images with bps < 8, but we also use it for
8 bps grayscale images to detect if MINISWHITE needs to be converted.

So, let's always set tiff_mode for PALETTE, MINISBLACK and MINISWHITE.

(cherry picked from commit 2e4b9bcb)

generated by matlabs blocproc function

Based on the suggested solution by Massimo, we should not compute the
remaining pixels per line but only at the end of the whole block, be it
tile or scanline.

I have not been able to find bw or palette examples that use load_separate
instead of load_contiguous, so that case is not tested. But, it also
doesn't make much sense to have planar when you have just one plane.

(cherry picked from commit 94de89fe)

In a previous commit 1, 2 and 4-bit B/W images were converted to grayscale.
However, it seems that there is more of a use case for these images to be
handled as indexed, even though technically they can be considered
grayscale.
Also, the only way to export these images again in the same format, is to
have them as indexed.

So, let's change this back, so that these kind of images will be opened
as indexed. With a reminder that in the future we could add an option
at loading time where the user can choose whether they prefer it to be
loaded as indexed or grayscale.

We use grayscale mappings, that we moved in the previous commit, to
add a palette to these grayscale images.

(cherry picked from commit 3e623703)

In preparation of using some of them earlier, we move the variables
used for grayscale mapping of 1, 2 and 4-bit per pixel images to the
top of file-tiff-load.

(cherry picked from commit 11ef2e44)

# Conflicts:
#	plug-ins/file-tiff/file-tiff-load.c