Fixed bug CORE-4212 : Dropping FK on GTT crashes server

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@58594 65644016-39b1-43b1-bf79-96bc8fe82c15
Fixed bug CORE-4214 : GTT should not reference permanent relation

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@58596 65644016-39b1-43b1-bf79-96bc8fe82c15
Fixed CORE-4204 - Error when compiling the procedure containing the statement if (x = (select ...)).

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@58599 65644016-39b1-43b1-bf79-96bc8fe82c15