[dataimport] Allow to replace escape char in the create_copyfrom_buffer

[doc] fix function name FTIRANK

[json] enable jsonexport selection on empty rsets (closes #2544358)

[test] fix req default value handling in CubicWebTC.view (closes #2544376) It's no more than the standard ``if rset`` vs. ``if rset is None`` error.

[ajax] fix attribute lookup (closes #2491038)

[server] add debugging for Hooks & Operations (closes #2470048)

[dataimport] Add SQL Store for faster import - works ONLY with Postgres for now, as it requires "copy from" command - closes #2410822 This store will use: - copy from for massive insertions. - execute from for update. The API of this store is similar to the other stores.

[test] swap order in assert of `test_users_and_groups_non_readable_by_guests` unittest2 order is (expected, got), not the opposite. This help test report readbility.

[test] fix server/querier/build_descr1 test. There is no self.transaction of TestCase. I assumed the test writer meant a session. This seems to make the test pass.

[server] make `test_bfss_fs_importing_transparency` less verbose on failure Dumping the whole content of a file on failure is a bit annoying. We only print the bad version here (it's usually the file path).

[entity] drop redundant cache update This ``cw_attr_cache`` update is redundant, ``_cw_update_attr_cache`` already do this step.

[cw-ctl] silence msgcat and msgfmt (closes #2527594)

Added tag cubicweb-debian-version-3.15.7-1 for changeset c5400558f370

Added tag cubicweb-version-3.15.7 for changeset d8916cee7b70

prepare 3.15.7

[migration] fix crash when adding a new meta relation type. Closes #2532483

[ldapfeed] fix connection leak (closes #2532528)

[zmq] add an introductive docstring on ZMQComm

[server config] on quick start, system source is still activated. Closes #2535714

[web] use `inline` `Content-Disposition` by default (closes #2535734) since known time we have been serving static file with a `filename` parameter on the `Content-Disposition` header. But since d74addac92bb we explicitly serve file as attachment if a filename is provided. However this is valid to have `inline` disposition and `filename` parameter. This changeset revert this part of d74addac92bb, going back to `inlined` by default. `IDownloadable` code explicitly request `attachment` content to preserve expected behavior.

[web] allow configuration of the Content-disposition value The `set_content_type` function now takes and optional `disposition` parameter to control the value of this HTTP header. Use of `Content-disposition: inline` with a filename parameter are valid, so the presence of filename does not allows to choose between `attachment` and `inline`

[downloadable] fix filename HTTP header for simple name with space (closes #2535715) Since d74addac92bb, we export simple ascii filename without any encoding in the `filename` parameter of the `Content-Disposition` header. If this name contains space this will fails, the parameter value will be truncated at the space position. (eg. `filename=jungle babar.txt` read as `jungle`) We need to quote the filename to prevent this (eg. `filename="jungle babar.txt"`). Then literal quote and backslash needs to be escaped too. The new escaping is correct according this extensive test case data base: http://greenbytes.de/tech/tc2231/

merge fixes from stable

Added tag cubicweb-debian-version-3.15.6-1 for changeset b05e156b8fe7