Made non-indexed distinct use a set.
Might be working, but serialization is borked.
Working on serialization.
Revert "Working on serialization."

This reverts commit 2d39942fec803d93720d7830461d6970de250350.
Revert "Revert "Working on serialization.""

This reverts commit 01536b11ffb9b1a95f4b87cd4f3b6235acffc025.
Fixed serialization in typed.hpp.
Streaming distinct works.
Removed RSI.
Removed RSI.
Fixed .distinct(index:'id')
fixed typed.hpp in release mode
Removed static_assert.
Removed useless forward-declaration.
Ruby and JS tests for distinct
Initial Python distinct impl.
fixing uninitialized scoped_ptr_t in alt cache
Added RDB_DECLARE_SERIALIZABLE in place of explicit template declarations.
Merge branch 'next' into mlucy_indexed_distinct
Merge branch 'grey_issue_2644' of github.com:rethinkdb/rethinkdb into mlucy_indexed_distinct
Update tests for Python driver.