fix #H4146 - more enlightenment vs drain resistance

Duplicate of another recent report as far as drain resistance from
Excalibur/Stormbringer/Staff of Aesculapius not being shown by
enlightenment goes, but this one mentioned that it also wasn't being
shown for lycanthropy.  Being inflicted by that does confers level-
drain resistance.  were_change() wasn't calling set_uasmon() since
it isn't changing youmonst.data, but set_uasmon() is were intrinsics
conferred by creature form are set up.  So call it when changing
were-form.  Direct access to u.ulycn wasn't calling it either, so add
a new routine to assign the value to that instead doing so directly.

src/potion.c

@@ -604,7 +604,7 @@ register struct obj *otmp;
                          makeplural(mons[u.ulycn].mname));
                     if (youmonst.data == &mons[u.ulycn])
                         you_unwere(FALSE);
-                    u.ulycn = NON_PM; /* cure lycanthropy */
+                    set_ulycn(NON_PM); /* cure lycanthropy */
                 }
                 losehp(Maybe_Half_Phys(d(2, 6)), "potion of holy water",
                        KILLED_BY_AN);