Previously using a generic mimetype handler failed when any kind of select= was given, because
we tried to cast the select-result to the original table type. With this change, this cast is
only applied when select=* is given implicitly or explicitly. This is the only case where this
makes sense, because this guarantees that correct columns are selected in the correct order for
this cast to succeed.
Resolves#3160
* test text/html and drop HtmlRawOutputSpec.hs
* all tests passing, removed all pendingWith
* make functions compatible with pg <= 12
* move custom media types tests to own spec
* anyelement aggregate
* apply aggregates without a final function
* overriding works
* overriding anyelement with particular agg
* cannot override vendored media types
* plan spec works with custom aggregate
* renamed media types to make clear which ones are overridable
* correct content negotiation with same weight
* text/tab-separated-values media type
* text/csv with BOM plus content-disposition header
