fix for Tcl 8.7: - when recreating an nsf object in in tcl 8.7, we seem to have to invalidate the intrep, otherwise the new command is not picked up by a later Tcl_GetCommandFromObj()
* nsf.c (NsfMethodAliasCmd): Tcl 8.7 is more picky about typePtr and intrep being in line. We need to NULL the typePtr explicitly. TclFreeIntRep does so for us as good Tcl citizens, rather than setting bodyObj->typePtr == NULL directly.