Fixed bug CORE-4372 : Deadlock is possible when two data pages contains record fragments pointing to each other

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@59311 65644016-39b1-43b1-bf79-96bc8fe82c15
Fixed bug CORE-2848 : "lock conversion denied" or "lock denied" error

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@59312 65644016-39b1-43b1-bf79-96bc8fe82c15