[facet] add missing selector to HasRelationFacet

[facets] proper fix for #1625112: we should rather call unicode() as we always manipulate string as unicode internally

merge

[etwist] Generates apache's mod_concat-like urls for js and css Uses the lists of js, css and ie_css included in order to generate urls compatible with Apache mod_concat (ie: http://test.fr/??file1.js,file2.js). Css files may use `media` option or may be for IE only ; this patch does not concatenate css filenames for different media types or different IE specs. It concatenates only files served under cubicweb's `data` urls and keeps original include order. The generated urls are added to the HTML header as usual. HOW-TO: - calling HTMLHead(datadir_url) will enable the url concatenation - calling HTMLHead() will not benefit of url concatenation IMPORTANT NOTE: - fckeditor can no more be served under `/data/` segment

handle js/ css file concatenation with twisted

put data version md5 into a new url segment to ease static serving

add cwctl command to generate a consolidated data directory with all cubes/ cubicweb data directories content to be delivered statically

[etwist] refactor child resources management

[vreg] vregistry._select_best was needlessly instanciating NoSelectableObject (closes #1626708) in large selections, this incurred a non negligible cost (add_relations with 2000 inlined relations runs 7% faster with this patch)

backport stable