fix avenger roof.
fix for confusion over distance funciton.
Zombies should spawn without TUs
remove unnecessary include.
Feature addition: Item Stacking in inventory screen.

only items that match can be stacked.
matching conditions:
- is the same item type. (uses the same ruleset)
- is loaded with the same type and amount of ammo. (including none at all)
- is not a live grenade.
- is not a corpse.
fix warning
Finish off item stacking

the intuitive bit.
remove some redundancy
Speed up patrol state.
fix silly typo
add screen centering Functions.

will adjust screens in higher resolution modes.
Delete some rogue timers.
center ALL of the screens.
Merge pull request #531 from MadAnd/master

Ukrainian translation maintenance
center intro on higher resolutions.
Fix typo in Ukrainian translation (vkravets).