macOS system language detection.

It appears the system language detection doesn't work on [some versions
of?] macOS.  Fixed.

Strangely, querying the Cocoa API for the system locale on a system in
US with the preferred language set to Korean produces the invalid locale
"ko-US" instead of the expected "ko-KR".  This behavior of returning the
language with a invalid region qualifier for the language appears to
happen only with languages where macOS does not have regional variants
(this issue does not seem to occur with Canadian English, en-CA, for
example.)  A fuzzy matching locale function has been added to handle
this issue.

src/ios.h

@@ -24,6 +24,7 @@
 
 
 void apple_init(void);
+const char *apple_locale(void);
 const char *apple_fontsPath(void);
 const char *apple_preferencesPath(void);
 const char *apple_globalPreferencesPath(void);