[schema] stop using RQLUniqueConstraint (closes #3753250) The last uses are replaced with unique together constraints.

[dataimport] Have ucsvreader's API match that of csv.reader (closes #3705701) 'separator' and 'quote' are replaced with 'delimiter' and 'quotechar'.

[utils] Add a '_cwtracehtml' GET parameter to trace self._cw.w() calls (closes #4601327) The core of this patch is in UStringIO.write(). When tracing is enabled, write() doesn't just append the 'value' argument to the underlying list. Instead, a stack trace is recorded and a special HTML "source" is formatted. The output with tracing enabled is an HTML page, with the original HTML escaped, and made clickable to show the stack trace when the write() call was done. This allows answering the recurring question: "who wrote this tag here?!"

[datafeed] Add a raise_on_error parameter to DataFeedSource.extid2entity And pass the option from various `process_` methods in existing parsers. This makes debugging in tests easier. Closes #4601191.

[test/view forms] use the official, undeprecated API

[rset] kill the rset._rqlst cache Right now it "works" for the standard, internal uses. However when we will fold ClientConnection and Connection, it will hurt, because suddenly we get more cache hits, and the following situation would become commonplace: * there is an un-annotated _rqlst given by the querier * some view (e.g. facets) requests the .syntax_tree, which takes a copy of _rqlst * the view actually expects the rql syntax tree to be annotated, but it was not, hence we crash. Related to #3837233.

[source/native] session -> cnx Also swap process_results arguments order to make cnx come earlier.

[hookstests] change got/expected order

[config] kill a getattr

[tests/web] switch previous commit (136b5f995f8) to the new test api Related to #3670209.