Moved quantile_freq to wt_algorithm

- moved empty(range_type) to wt_helper
- added size(range_type) operation
- moved topk_qprobing to doc_list_index_qprobing
Moved quantile_freq to wt_algorithm
Added raw member to allow serialization of

int_vector without size header.
Fixed compiler warning.
Fixed qprobing code.
Added tests for algorithms in wt_algorithm.hpp

Refined intersect (results are ordered according to
value if underlying WT is lex_ordered)
Addressed unused parameter warning.
Merge pull request #146 from simongog/wt_housekeeping

Move some general wt_int methods to wt_algorithm