Track how many bytes we skip in each lexical comparison and don't check
prefix bytes we know will match.
Merge pull request #595 from wiredtiger/offsetsearch

Track how many bytes match in each lexical comparison and don't check prefix bytes we know will match.
Track how many bytes we skip in each lexical comparison and don't check
prefix bytes we know will match on leaf pages, not just internal pages.

Add a comment to try and explain what's going on with skiphigh/skiplow.

Reference #595.
Merge branch 'develop' into branch592

Conflicts:
	src/btree/row_srch.c
Enhance a comment.