`VersionSchema#relation` uses `fetch` and `to_s`.
`CellType#from_key_value_and_qualifier` returns schema name symbols.

..and not the schema objects themselves.  This makes
inspecting/copying/pasting somewhat easier.  The layout is also
changed to put the row key first.  These make the results of gets and
scans look somewhat more like puts.
Drop the crud helper in favor of using the relation client.

`fixture` takes a relation name instead of a table name, and the
yielded block should return an array.  Each element should be of the
form:

`[row_key, qualifier_name, qualifier, value, timestamp]`

These are each translated to a `Put` and written.

`expect_table` has become `expect_relation`, the expected rows have
been pushed down to a block where they should resemble the rows
received from `Relation#scan` after `flatten(1)`.

`expect_relation` also now takes qualifier name-value pairs, to select
just those columns that are actually in the desired relation.

The content of the blocks in `fixture` and `expect_relation` have
identical structure, and should be interchangeable.