Rewrote WebPPictureHasTransparency() to use them (even for argb).
This is 10% faster, for some reasons.
SSE2 version should be straightforward.
Removes a TODO.
Change-Id: I7ad5848fc5e355e2df505dbcd5a0f42fb6cbab41
Half of the functionality was duplicated.
The rest is about the alpha channel handling so we
might as well put it in the appropriate file.
Change-Id: I8d5ef0afce82cc4842ab7132fd97995c42e6140a
this avoids duplicates between these trees and dsp/, e.g., enc/tree.c,
dec/tree.c, making pulling the whole library source tree into one target
possible
BUG=webp:279
Change-Id: I060a614833c7c24ddd37bf641702ae6a5eef1775
