FreeImage: myriad more PNG patches

1-bit images should now be covered in every possible format, including
all tRNS chunk variations.

16-bit grayscale + binary alpha are now covered.

<= 8-bit grayscale with tRNS are now covered much more reliably.  I
*think* all variations are covered, but with PNG, it's hard to know.
Win 7 specific features update

I've spent some time investigating potential fixes to this issue, and
short of simply not releasing the interface (which may be a valid
option??), I can't find a fix that prevents crashes under DEP.  I'm
leery about not manually releasing the interface since we allocate it on
the heap and I'm not 100% certain that it self-releases, but perhaps
future investigations will reveal that as a valid option.

In the meantime, however, progress bar updates in the Win 7 task bar are
no longer available.  :(