Windows only changes:
- try to load DLL's from fbclient's folder if DLL's file name contains no full path 
- if attempt above failed, load DLL using given file name (as is)
- cleanup

It should fix CORE-4275 (create database fault if fbclient.dll loaded from another directory (Providers = Engine12))

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59133 65644016-39b1-43b1-bf79-96bc8fe82c15