1. Improvement CORE-4431 : Reduce contention for allocation table lock while database is in stalled physical backup state
2. Improvement CORE-4432 : Let attachments to not block others when allocation table is read first time
3. On Windows, file can not be deleted while system writes cached data into it, even if file is not open by anyone.
Therefore flush delta file implicitly before closing it.


git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@59592 65644016-39b1-43b1-bf79-96bc8fe82c15
Fixed bug CORE-4433 : GlobalRWLock could not downgrade EX lock to SH if readers is present

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@59593 65644016-39b1-43b1-bf79-96bc8fe82c15