New switch for gbak

replace_database switch was dangerous , it was decided to be changed in this thread

From the firebird2 ChangeLog

1. New switch for gbak -RECREATE_DATABASE [OVERWRITE].
Simple RECREATE_DATABASE is equal to CREATE_DATABASE,    
RECREATE_DATABASE OVERWRITE is equal to REPLACE_DATABASE.  
2.gbak uses isc_dpb_overwrite to create database over existing files 
3.engine overwrite existing files only if asked explicitly by    
user by setting isc_dpb_overwrite to 1 
4.fixed unregistered bug - when gbak uses service manager and passed  
command line contains invalid switch. Service reports error and  finish 
but not call Service::svc_started therefore response is not send and gbak 
is stalled forever