* generator/*Gen.cs : add ToNativeReturnType to deal with the g_free string nonsense in the virtual method case. svn path=/trunk/gtk-sharp/; revision=36289
* generator/GStringGen.cs : new generatable impl for GStrings. * generator/InterfaceGen.cs : better error reporting. * generator/Makefile.am : add new source file. * generator/Method.cs : better error reporting. * generator/SymbolTable.cs : add new GString igen. svn path=/trunk/gtk-sharp/; revision=34525