Fixed BULK_READ server implementation

Implementation must not send ack with error if not all requests failed
Added session::find_any_indexes

Find any implements OR paradigm in addition to old AND one.
session::find_indexes renamed to session::find_all_indexes
Returned 2.20.*.* namespace behaviour

Now algorithm is hash(namespace + '\0' + key) if namespace is set
and hash(key) otherwise
Merge pull request #137 from euroelessar/master

Fixed BULK READ, added OR-logic for indexes finding, changed namespace behaviour