nightly update

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@57984 65644016-39b1-43b1-bf79-96bc8fe82c15
Finish MERGE improvements documentation (CORE-2005, CORE-3020, CORE-3639).

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@57987 65644016-39b1-43b1-bf79-96bc8fe82c15
Docs.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@57988 65644016-39b1-43b1-bf79-96bc8fe82c15
Make it resistant to races (avoid violating array boundaries)

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@57989 65644016-39b1-43b1-bf79-96bc8fe82c15