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/pcedit/pc.appleevents.mm

@@ -18,6 +18,7 @@ typedef NSAppleEventDescriptor AEDescr;
 -(void)handleQuit:(AEDescr*)theAppleEvent withReply: (AEDescr*)reply;
 @end
 
+void set_up_apple_events(); // Suppress "no prototype" warning
 void set_up_apple_events() {
 	AppleEventHandler* aeHandler = [[AppleEventHandler alloc] init];
 	NSAppleEventManager* AEmgr = [NSAppleEventManager sharedAppleEventManager];
@@ -29,9 +30,13 @@ void set_up_apple_events() {
 
 @implementation AppleEventHandler
 -(void)handleOpenDoc:(AEDescr*)theAppleEvent withReply: (AEDescr*)reply {
+	(void) theAppleEvent; // Suppress "unused parameter" warning
+	(void) reply;
 	// TODO: Handle this
 }
 -(void)handleQuit:(AEDescr*)theAppleEvent withReply: (AEDescr*)reply {
+	(void) theAppleEvent; // Suppress "unused parameter" warning
+	(void) reply;
 	All_Done = verify_restore_quit(0);
 }
 @end