Implementation and stability patches

This pull request contains:
 - Implementation for RopModifyRecipients request with partian x500dn
 - fixed use-after-free in EcDoRpcExt2 function
 - this commit allow for uses like:
   openchange_newuser --create --enable 'kcurtis'
 - check for return value for emsmdbp_object_open_folder_by_fid() in EcDoRpc_RopSyncImportHierarchyChange()
Perhaps not something for this pull request (I see you're just moving this code), but it would be nice if 0 and 2 had constants for them so they were more readable.