fix for sets/mar2014/..317minimized..

Observed behavior:
  --check-model failed for set-term (union (z3f69 z3v151) (setenum z3v143))
with different set of elements in the model for representative and the node
itself.

Issue:
  The trouble with data structure being mainted to ensure that things
for which lemmas have been generated are not generated again. This
data structure (d_pendingEverInserted) needs to be user context
dependent. The bug was in the sequence of steps from requesting that
a lemma be generated to when it actually was. Sequence was:
addToPending (and also adds to pending ever inserted) ->
isComplete (might remove things from pending if requirment met in other ways) ->
getLemma (actually generated the lemma, if requirement not already met)

Resolution:
  adding terms to d_pendingEverInserted was moved from addToPending()
to getLemma().