Ales,
so, short answer is "AbstractIgnoreFilesDeployer is not available in JBoss AS 5.1, since JBoss AS 5.1 uses vfs-deployers-spi v 2.0.7" .
To come back to this 6 month old issue, it cannot be worked around as is with jboss-ignore.txt in JBoss AS 5.1.
I will try to use the 2.0.10 with JBoss AS 5.1 to check anyway.