Use standard library style members of wxArrayString (and wxString) ...

... which will make it easier to change the types of those containers to
std::vectors of other string-like classes

for wxString,

IsEmpty => empty
Clear => clear
Alloc => reserve

for wxArrayString,

Count => size
GetCount => size
IsEmpty => empty
Add => push_back
Clear => clear
Empty => clear
Sort => std::sort (only with default comparator)
SetCount => resize
Last => back
Item => operator []
Alloc => reserve

src/FileFormats.cpp

@@ -220,7 +220,7 @@ wxArrayString sf_get_all_extensions()
       sf_command(NULL, SFC_GET_FORMAT_MAJOR,
                  &format_info, sizeof (format_info)) ;
 
-      exts.Add(LAT1CTOWX(format_info.extension));
+      exts.push_back(LAT1CTOWX(format_info.extension));
    }
 
    // Some other extensions that are often sound files