• Replaced several := ops with their += equivalents; the old form became unnecessary with the bsd.prog.mk,v 1.69 change.

• Eliminated duplicate y.tab.h in SRCS.

Reviewed by: bde

• Complementary to the said bsd.prog.mk change, use the fact that inner .for loops are not real loops but a tricky form of a local macro for the outer loop's variable, and switch to using faster variable modifiers to replace extensions.