master()->add_predefine()

[Henrik Grubbstr�m (Lysator) @ Pike (-) developers forum]

I've now updated Pike_7_4_master to contain all symbols that I found
when diffing the real Pike 7.2 and Pike 7.4 masters. Left to do is to
do the same for the Pike_7_6_master, and to check against the masters
of real running Pike's 0.6 through 7.6.