these searchers incorrectly called Next() on their underlying
searcher, instead of Advance(). this can cause values to be
returned with an ID less than the one that was Advanced() to,
which violates the contract, and causes other incorrect behavior.
fixes#342
regexp, fuzzy and numeric range searchers now check to see if
they will be exceeding a configured DisjunctionMaxClauseCount
and stop work earlier, this does a better job of avoiding
situations which consume all available memory for an operation
they cannot complete
