Passing through images with inverted color doesn't seem right
Add saving support for YA8 and YA16 images

It seems to work, but it still does not specify ExtraSamples
tag to state that stored data is in fact an alpha channel.
See bug #56 .
Add reading of YA tiff images

This code does not check that the extra channel is in fact
a transparency channel
Use proper bit expansion

Expanding from lower bits per pixel to higher bits per pixel
should fill all the bits by cycling the original ones.
Add test images for tiff YA8 and YA16

Currently, the YA16 version isn't properly loaded in the bottom
40% properly. I don't know why.
comment truncation of greyscale 32bit images
Merge pull request #60 from iger/tiff2

Fix color scaling in tiff loading