Merge [2121], [2122], [2123], [2124], [2125], [2126], and [2127] from trunk.
[2121]: Mark gen_x86_insn.py outputs as generated.
[2122]: Don't read past end of string in parsers (not bug).
[2123]: Fix expression simplification bug.
[2124]: Warn if unused groups are detected in gen_x86_insn.py.
[2125]: VPBLENDVB doesn't have a 256-bit form; remove it.
[2126]: Generate GOTPCREL relocation for [rel foo wrt ..gotpc].
[2127]: Optimize non-strict push with 66 override to byte size if possible.
svn path=/branches/yasm-0.7.x/; revision=2148
