Backed out the micro-optimization in 1.4. It was to help gcc-2.6.3

Backed out the micro-optimization in 1.4.  It was to help gcc-2.6.3
on i486's (and probably i386's), but it has had very little effect
since gcc-2.7 or gcc-2.95.  With gcc-3.3, it gave a small
pessimization for at least i386's, athlon-xp's and pentium4's, a
small optimization (I think) for pentium1's, and made no difference
for i386's.  (movzbl is best for all the later processors, and the
micro-optimization was to stop it being used on i486's.)