Nuke as many warnings as possible, and several globals as well

- Warnings completely suppressed for the included TinyXML and gzstream libraries
- Parentheses warnings are now errors, since there were several that looked like bugs
- Ditto for dangling else warnings

Some of these warnings were actually bugs:
- Town wandering monsters would have never spawned, because the code to do so was accidentally nested within a check for overall_mode == MODE_OUTDOORS
---> boe.monster.cpp, lines 105-137
- Monster's behaviour with respect to elemental fields did not correctly depend on their immunities (this is the same precedence issue Sylae messed up fixing in the Windows code)
---> boe.monsters.cpp, lines 345-359
- Display of damage blocked by armour appeared to be incorrect (needs verification)
---> boe.newgraph.cpp, line 1079
- Three-choice dialogs probably weren't dealing with unusual button types correctly, though that's a minor point since they aren't expected to use such buttons

osx/boe.locutils.cpp

@@ -70,10 +70,11 @@ bool point_onscreen(location center,location check)
 
 short set_direction (location old_pt, location new_pt)
 {
-	if (old_pt.x == new_pt.x)
+	if (old_pt.x == new_pt.x) {
 		if (old_pt.y > new_pt.y)
 			return DIR_N;
 		else return DIR_S;
+	}
 	if (old_pt.x > new_pt.x) {
 		if (old_pt.y > new_pt.y)
 			return DIR_NW;