Use C locale for numbers in wx(File)Config.

Using the current locale decimal point in config files results in problems
when moving the files to another machine or even using a different locale on
the same one, so don't do it.

Always write the numbers using C locale and try to read them in C locale too
first, but also try the current locale if we failed for backwards
compatibility and to be tolerant with users who edit their config files by
hand.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64450 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/config.h

@@ -689,6 +689,14 @@ public:
     /**
         Writes the double value to the config file and returns @true on
         success.
+
+        Notice that if floating point numbers are saved as strings (as is the
+        case with the configuration files used by wxFileConfig), this function
+        uses the C locale for writing out the number, i.e. it will always use a
+        period as the decimal separator, irrespectively of the current locale.
+        This behaviour is new since wxWidgets 2.9.1 as the current locale was
+        used before, but the change should be transparent because both C and
+        current locales are tried when reading the numbers back.
     */
     bool Write(const wxString& key, double value);
     /**