[LyX/master] Use string value rather than int for \language_package_selection pref

[Udi Fogiel]

Jürgen is this a stray break?

-                       os << "\\language_package_selection ";
-                       switch (language_package_selection) {
-                       case LP_AUTO:
-                               os << "0\n";
+                       os << "\\language_package_selection \""
+                           << language_package_selection
+                           << "\"\n";
                                break;

it gives me problems when I try to switch a UI language from the GUI.

Udi