Backported dbkey/recver optimization.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@57616 65644016-39b1-43b1-bf79-96bc8fe82c15
This trivial optimization saves a few percents of performance when reading/writing DBKEYs from/to compatible local variables.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@57617 65644016-39b1-43b1-bf79-96bc8fe82c15
Slightly improved the condition for the Adriano's backward compatibility workaround, this optimizes METD_move() into a plain memcpy() for strings with an explicitly declared charset.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@57619 65644016-39b1-43b1-bf79-96bc8fe82c15