Fixed possible deadlocks between a worker thread and an attachment-level AST.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59961 65644016-39b1-43b1-bf79-96bc8fe82c15
Atempted to fix a crash when the database monitoring is used concurrently under load.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59962 65644016-39b1-43b1-bf79-96bc8fe82c15