ADQL: Fix an ADQL bug (raised by Dave Morris) in the management of subqueries: before, it was impossible to use (in a clause different from the FROM) columns of a father query inside a subquery.

Becareful with the function addMatch(ADQLObject, ADQLIterator): the iterator may be null if the match to add is the root search object itself!
No modification needed in SimpleReplaceHandler: Null test already done :-) !

TAP: Fix incorrect XML format: the INFO for PROVIDER was not ended properly => an error was raised by TOPCAT when a Java error was occuring in TAP or in a query execution.

ADQL: Completely change/improve Joins management, and particularly NATURAL JOIN and USING JOIN. Now, every joined columns are represented by a DBCommonColumn instance which has a given table coverage.
Before, there was a problem while using at least 3 or 4 NATURAL JOINs. Bug raised by Menelaos Perdikeas (ESAC).

(1) Missing contains(Object) function. Without this function, any ArrayList function like retainAll(...) did not work properly: the research in the collection was made with a bad key. KeyExtractor was not used.
(2) Result of a research (function get(...)) must return a copy of the result, since the result is an ArrayList, value of the HashMap used for research. If a copy is not returned, any modification (and particularly remove(...)) can be made on the value of the index (HashMap) used for the research.

TAP: Test better the JDBC connection URL: several syntaxes are possible. Here, the following syntax did not work before this correction: jdbc:postgresql:database (only if it is a local database). Only jdbc:postgresql://host/database and jdbc:postgresql://host:port/database worked!
TODO Parsing of JDBC connection URL should rather be checked again!

ADQL: Fix ArrayIndexOutOfBoundsException while initializing a DefaultUDF (User Defined Function) object with several parameters.