Change gridStartIterate interface to safely allow recursive calls.

Probably fixes ticket:3894.
qtscript: Fix a typo in structure health calculation. Fixes ticket:3930.
Merge branch 'bugfixes'

Conflicts:
	src/ai.cpp
	src/combat.cpp
	src/mapgrid.cpp
	src/mapgrid.h
	src/projectile.cpp
	src/qtscriptfuncs.cpp