Add more black-box tests for PlainTable and explicitly support total order mode

Summary:
1. Add some more implementation-aware tests for PlainTable
2. move from a hard-coded one index per 16 rows in one prefix to a configurable number. Also, make hash table ratio = 0  means binary search only. Also fixes some divide 0 risks.
3. Explicitly support total order (only use binary search)
4. some code cleaning up.

Test Plan: make all check

Reviewers: haobo, kailiu

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16023
Fix table_reader_bench and add it to "make"

Summary: Fix table_reader_bench after some interface changes. Add it to make to avoid future breaking

Test Plan: make table_reader_bench and run it with different options.

Reviewers: kailiu, haobo

Reviewed By: haobo

CC: igor, leveldb

Differential Revision: https://reviews.facebook.net/D16107