* make ALPHNew/Delete static
* properly init ALPHDec::io_
* introduce AllocateAlphaPlane() and WebPDeallocateAlphaMemory()
* reorganize VP8DecompressAlphaRows()
but we're still allocate the full alpha-plane. Optim will come
in another patch since it's tricky
Change-Id: Ib6f190a40abb7926a71535b0ed67c39d0974e06a
+ split AllocateInternalBuffers() into two 32b/8b variants instead of
trying to do everything in one function.
Change-Id: I35cac9fcd990a2194c95da4b2a4046ca3a514343
