[book] Improve PostgreSQL configuration section * Do not advice for specific PostgreSQL version (point to meta-packages if available in Linux distros); * First mention packages from Linux distros, put the link to official postgres documentation at the end; Closes #2725302.

[js] add a selector string escaping function will help use id strings in jquery selector expressions, e.g: "foo.[subject]:42" -> "foo\.\[subject\]\:42" Related to #3154531.

[merge] backport stable fixes

[test/ldapsource] backout 192a748550c7 which broke RQL2LDAPFilterTC

[rset] make sure rset.description is always a list It's more consistent, and avoids pylint warning "Instance of 'tuple' has no 'append' member"

[schema] edit syntax tree instead of playing with strings for RQLExpressions Lets us support more complex expressions involving e.g. "HAVING" clauses. Closes #3202855

[py3k] note about future warning on __eq__ vs __hash__ Closes #3179561.

[formfields] py3k kill future compat warning Related to #3179561.

[entity] do not raise an AssertionError if the kwargs given to set_relations/attributes is empty Regression was introduced in 3.16 with the new cw_set API. Old set_relations and set_attributes methods did not crash on empty kwargs. Closes #3104019.

[packaging] setup.py: don't exclude skeleton/debian/* from being installed Closes #3192725.

[tests/hooks/integrity] kill old and empty skipped test

[server/session] demote log to debug It can pollute the log very fast. Closes #3203391.