Firebird 2.5.6 Sub-release

This sub-release comes with a few bug fixes and a couple of improvements:

Run-time errors raised inside EXECUTE BLOCK now provide the location context (line and column numbers). Backport from Firebird 3 by D. Yemanov. For more info, see Tracker ticket CORE-5216.
Previously, when a restore failed to activate and recreate a deferred index, typically because of insufficient temporary disk space, gbak would return a non-zero completion code (“FAIL”) only when the failure affected a referential constraint. Now, gbak returns a fail code for any index that fails the activate-and-rebuild step. This improvement should be particularly helpful where backups and restores are managed using scripts, enabling indexes left inactive after the restore to be caught and corrected.