Update WorldFacts project with Xcode 4.6 Build Settings

The following additional compiler warnings are now enabled:

  CLANG_WARN_CONSTANT_CONVERSION = YES
  CLANG_WARN_EMPTY_BODY = YES;
  CLANG_WARN_ENUM_CONVERSION = YES;
  CLANG_WARN_INT_CONVERSION = YES;
  CLANG_WARN__DUPLICATE_METHOD_MATCH = YES;