* RDB$BLOB_UTIL system package.
* Do not checkout from engine when calling system packages.
* Remove usage of Attachment::SyncGuard in RDB$BLOB_UTIL.
* Fix Windows build.
* Fix RDB$BLOB_UTIL.SEEK.
* Fix crash.
* Rework changing routines and names for better fit after creation of BLOB_APPEND.
* Add RDB$BLOB_UTIL.IS_WRITABLE function.
* Misc.
* Fix documentation.
* Re-add and use RDB$BLOB_UTIL_HANDLE domain.
* Rename domain RDB$LONG_NUMBER to RDB$INTEGER.
