Split European Spanish and Latin American Spanish

This is a test split per requests.  While "Latin American Spanish" is
not really homogeneous, there are distinct differences to European
spanish, so we are splitting in an effort to allow both translations.
If one is less viable, this may re-merge in the future.

common/pgm_base.cpp

@@ -77,6 +77,7 @@ LANGUAGE_DESCR LanguagesList[] =
     { wxLANGUAGE_GREEK,      ID_LANGUAGE_GREEK,      wxT( "Ελληνικά" ), true },
     { wxLANGUAGE_ENGLISH,    ID_LANGUAGE_ENGLISH,    wxT( "English" ),  true },
     { wxLANGUAGE_SPANISH,    ID_LANGUAGE_SPANISH,    wxT( "Español" ),  true },
+    { wxLANGUAGE_SPANISH_MEXICAN, ID_LANGUAGE_SPANISH, wxT( "Español (Latinoamericano)" ),  true },
     { wxLANGUAGE_FRENCH,     ID_LANGUAGE_FRENCH,     wxT( "Français" ), true },
     { wxLANGUAGE_KOREAN,     ID_LANGUAGE_KOREAN,     wxT( "한국인"),       true },
     { wxLANGUAGE_ITALIAN,    ID_LANGUAGE_ITALIAN,    wxT( "Italiano" ), true },

include/id.h

@@ -120,6 +120,7 @@ enum main_id
     ID_LANGUAGE_FRENCH,
     ID_LANGUAGE_FINNISH,
     ID_LANGUAGE_SPANISH,
+    ID_LANGUAGE_SPANISH_MEXICAN,
     ID_LANGUAGE_GERMAN,
     ID_LANGUAGE_GREEK,
     ID_LANGUAGE_NORWEGIAN,

translation/pofiles/LINGUAS

@@ -8,6 +8,7 @@ de
 el
 en
 es
+es_MX
 fi
 fr
 hu