fix #H4142 - resistance from Excalibur

fix #H4142 - resistance from Excalibur

Enlightenment and end of game disclosure didn't report level-drain
resistance if that was obtained via wielding Excalibur (or Stormbringer
or Staff of Aesculapius).  Drain_resistance wasn't one of the attributes
set for intrinsics/extrinsics when wielding or unwielding weapon or
wearing/unwearing other equipment.  loseexp() checks resists_drli()
which does check for items in use, so level drain would be aborted,
possibly after messages claimed that it was taming place.  I didn't try
to untangle any of that, just changed set_artifact_intrinsic to include
a test for DRAIN_RES.