Have 'makedefs -m' output default mons[].difficulty values in the
stub 'monstr.c' that still gets generated for that option. It
would be better to allow specifying which monsters are of interest
but I didn't want to get bogged down by interface issues.
I needed it for mons[PM_ELF].difficulty after changing that monster's
level, so it still has a purpose. Code is from 3.4.3, reformatted
manually.
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