<Someone> noticed that the change to require axes for trees (and allow them for
doors) did not extend to monsters. Now it does.
- added 2 new weapon check flags to handle the new cases
- added some detailed digging flags to mfndpos, based on ALLOW_DIG, and
moved some common logic regarding that flag into mfndpos
- made the ARMS check consistent for 2-handed weapons
I also noticed that simply carrying a pick was enough to allow a monster to
dig a door; wielding wasn't required. This is fixed as well.
