Have makedefs do through a common point when exiting, in case it ever
needs extra memory or scratch file cleanup.
While testing, I discovered that the reference use of 'makedefs -o' to
build obsolete onames.h didn't work anymore because of the change to
not require object probabilities to add up to 1000 within classes.
I think fixing that is the only change besides new 'makedefs_exit()'.
cca90a061c