Really fix quantization factor allocation

Actually allocate less (instead of just initialize less) and fix comments.
x86: Pass -Worphan-labels to yasm

Makes it easier to detect typos.
x86inc: Support arbitrary stack alignments

If the stack is known to be at least 32-byte aligned we can safely store ymm
registers on the stack without doing manual alignment.

Change ALLOC_STACK to always align the stack before allocating stack space for
consistency. Previously alignment would occur either before or after allocating
stack space depending on whether manual alignment was required or not.
Merge branch 'plain' into tMod