Upgrade to HSQLDB 2.6.1

21 October 2021 - version 2.6.1
-- version 2.6.1 is a bug fix release
-- added sql.lowercase_ident property for extra compatibility with PostgreSQL and MySQL unquoted identifier names
-- fixed an issue with performance of large updates in mvcc transaction mode
-- fixed an issue with query timeout settings
-- fixed a number of minor issues and regressions

21 March 2021 - version 2.6.0
-- Version 2.6.0 marks the 20th anniversary of HyperSQL.
-- The project maintainer would like to thank core developers Blaine Simpson, Campbell Burnet and Robert Preston for their contribution over many years, 
--    and all developers and users who contributed code, made useful suggestions, or reported issues.
-- version 2.6.0 main jar contains the module org.hsqldb and can be used as a Java module
-- version 2.6.0 jar requires JRE 11 or later - tested up to Java 16 RC
-- version 2.6.0 alternative jar requires JRE 8 or later
-- version 2.3.9 jar can be compiled with Java 6 (or 7) for JRE 6 and 7 and fully compatible with 2.6.0 except for the new JDBC features
-- The DatabaseManager class is no longer included in the Jars. Use DatabaseManagerSwing instead. 
-- added support for additional REGEXP_ functions.
-- added support for adding extra columns to FOREIGN KEY indexes; see ALTER CONSTRAINT in the Guide
-- added support for RECURSIVE_TABLE in WITH RECURSIVE queries
-- added system role SCRIPT_OPS for export / import of database structure and data
-- added extensive features to the collection classes in org.hsqldb.lib (maps, lists, queues etc.) which can also be used in user apps
-- improved MySQL syntax support for ENUM
-- fixed a number of regression in 2.5.1, e.g. use of MODULE for LOCAL TEMPORARY tables, truncated microsecond precision of java.sql.Timestamp values
-- fixed several minor issues
-- removed all use of Java (up to JDK 16) deprecated methods
-- revamped Ant and Gradle builds, now updated to latest Gradle