[repository api] definitly kill usage of word 'pool' to refer to connections set used by a session Also document session's data storage and some other internals. Hopefuly things will get clearer. Closes #1684860: vocabulary confusion in repository code: notion of 'pool'

if not rql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',
           ask_confirm=False):
    rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',
        ask_confirm=False)