Minor translation updates
Myriad new failsafe checks

These changes mostly consist of additional validations against things
like image ID, layer index, etc.  While these checks shouldn't
technically be necessary, they don't hurt, and I'd really like this PD
release to be as rock-solid as possible.
Color management: apply ICC profiles before converting to 32bpp
Asynchronous metadata parsing: improve reliability

When loading multiple images, the first image's metadata was sometimes
being lost due to the way image IDs were being detected.  Metadata
should now *always* be loaded correctly (if an image contains valid
metadata)
Asynchronous metadata parsing: additional debug checks