PUT to a column family should truncate it and replace the content

[boneill42]

This may be embracing REST semantics too much, but a PUT is technically supposed to replace the content of the resource at the URL with the content in the request.

For CFs, this would mean truncating the CF and then doing the same sort of thing as PATCH on the CF (described in the other issue I just posted).

The net effect of both issues would then be:

A PUT with no data on a CF ensures it exists and is empty.
A PUT with data on a CF replaces the content with the content of the request.
A PATCH with no data on a CF ensures it exists (but will not truncate it).
A PATCH with data on a CF works as described in my other issue.