Clean up math functions

- Remove checking for standard functions from the build system
- Prefix all invocations with std::
- Replace suffixed functions with unprefixed versions
- Include <cmath> in all files that use it and remove the global include

e.g. floorf(x) -> std::floor(x)

src/BGAnimation.cpp

@@ -107,14 +107,14 @@ void BGAnimation::LoadFromAniDir( const RString &_sAniDir )
 			// This is a 3.9-style BGAnimation (using .ini)
 			IniFile ini;
 			ini.ReadFile( sPathToIni );
-			
+
 			AddLayersFromAniDir( sAniDir, &ini ); // TODO: Check for circular load
-			
+
 			XNode* pBGAnimation = ini.GetChild( "BGAnimation" );
 			XNode dummy( "BGAnimation" );
 			if( pBGAnimation == nullptr )
 				pBGAnimation = &dummy;
-			
+
 			LoadFromNode( pBGAnimation );
 		}
 		else // We don't officially support .ini files anymore.
@@ -180,7 +180,7 @@ void BGAnimation::LoadFromNode( const XNode* pNode )
 /*
  * (c) 2001-2004 Ben Nordstrom, Chris Danford
  * All rights reserved.
- * 
+ *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the
  * "Software"), to deal in the Software without restriction, including
@@ -190,7 +190,7 @@ void BGAnimation::LoadFromNode( const XNode* pNode )
  * copyright notice(s) and this permission notice appear in all copies of
  * the Software and that both the above copyright notice(s) and this
  * permission notice appear in supporting documentation.
- * 
+ *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF