Fixed CORE-2119: Use entries in restrict list of ExternalFileAccess parameter to mangle filenames with relative path, also fixed assertion and diagnostics related to EXTERNAL FILE tables

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59470 65644016-39b1-43b1-bf79-96bc8fe82c15