[test] run unittest_migractions on postgresql sqlite's lack of support for a bunch of alter table functionality means some thing just don't get tested otherwise.

[devtools] Put pg sockets in /tmp Makes for shorter paths (limited by sockaddr_un). Also use the default port, since we're not listening on TCP sockets.

[devtools] change the way we start/stop postgresql Instead of having the test db handler start a cluster on demand, use the test module's setUp/tearDown callbacks to do it. This allows to have one data directory (and thus cluster) per test module, allowing different test modules to run in parallel, each using its own database cluster whose path is based on the test module.

[devtools] make test db name for postgresql process-specific In case we run two tests concurrently on the same cluster, better not use the same db name for both.

[devtools] extract functions to start/stop a postgresql cluster

[test] don't leave NULL columns around when making an attribute required It doesn't matter on sqlite (it doesn't do ALTER COLUMN), but when running this test on postgresql it fails to add the 'NOT NULL' constraint otherwise.

[server/session] Roll back in connection exit This was changed in commit 8b35a898b334 "[server] remove cnxset tracking, it is now unneeded". When exiting a CubicWeb Connection, the database connection is put back into the common pool. At that point anything done during the lifetime of the CubicWeb Connection needs to be committed or rolled back. Do a proper rollback to finish the transaction, as was happening before the above-mentionned commit. This showed up on testing with postgresql, when a DB schema modification was blocked by an old connection that was still "in transaction".

[web/views/formrenderer] do not use `cubicweb:target` attribute on form (closes #5534074) The `cubicweb:target` is a flag indicating that the form data (with file input) shall be posted inside an iframe - this is a well known "ajax-like" workaround to post files with browsers that do not support `FormData` (a.k.a IE<10). The `cubicweb:target` was introduced when CW used the "xhtml strict" doctype. Now that CW uses the "html5" doctype, this namespaced attribute is no longer necessary and the iframe can be generated directly. Before this patch, CW inserts the `cubicweb:target` attribute in the form DOM element (server side) and `setFormsTarget()` updates the DOM with a new `<iframe>` element (client side). Now, CW inserts the `<iframe>` DOM element directly (server side), making `setFormsTarget` useless.

[js] lint : make it explicit that typeof is an operator, not a function. Also, use === / !== except for null / undefined comparison

[devtools] qunit: show helpful data when an assertion fails Related to #5533333.