Isssue reported by Tomsod: hero-as-target section of mhitm_ad_phys()
was not handling hero's Half_physical_damage attribute.
The issue was about cloning a pet from hero who is poly'd into a
pudding but it was more general than that. Half_physical_damage was
ignored for any hit by a monster-wielded weapon against poly'd hero.
It took a while to convince myself that Half_physical_damage wasn't
aleady being applied elsewhere but it doesn't seem to be.
Fixes#1447
edd11009e9