Failing specs: new Post.search behaviour which ANDs the words, and only searches whole words (not substrings).
Implement new Post.search: search only for whole words, and AND the words.
Move search code into a HasSearchableText module.  Make Post class use it.
Failing specs for new way that search will work on comments.
Implement new way of searching (same as Post search).
Use PostgreSQL's full text search feature(s) instead of trying to code our own search by combining SQL subexpressions.