Fix bug#1264 - leave only underspecified lexemes if agreement exists only via them.

Underlying issue was temporary table of remaining lexemes for a token not being
updated (emptied) if only underspecified lexemes of the token met an agreement.
Effectively the token was left in its original state i.e. with all
original lexemes present, both those that were underspecified and the remaining
ones that did not met a weak agreement that was otherwise met via the
underspecified lexemes.