Make sure numeric conversions are not locale dependent

In [19024f72\lyxgit] this line was removed. Later this caused that floats were converted to strings using ','s instead of '.'s. Readding this line fixes this.

src/frontends/qt4/GuiApplication.cpp

@@ -188,6 +188,7 @@ void setLocale()
 	}
 	Messages::guiLanguage(fromqstr(theLocale.name()));
 	QLocale::setDefault(theLocale);
+	setlocale(LC_NUMERIC, "C");
 }