fix parsing of runas lists:

fix parsing of runas lists:
o oprunasuser and runaslist now return a value
o in a runasspec, if a runaslist does not return TRUE, set runas_matches to
  FALSE.  Normally, a runaslist only returns FALSE for explicitly denied
  users.
o since runaslist does not modify the stack there is no need for a push/pop
  in runasalias.