Monster on monster attacks

The "to hit" modifier corrections for monster weapons
when hitting another monster are wrong. The consequence
of this is that later attacks are much less likely to
suceed than the previous attack (there's supposed to be
a slight effect of this anyway, but this is
unintentional). A secondary effect is that the messages
re. "just missed" and blocking messages may also be
wrong.

To fix remove one of the duplicate corrections around
line 308 of mhitm.c and move the other one below the
call to missmm(). Check if there are any other
occurances.