Fixing compiler warnings in the posix-winsync plugin
    
    The commit b9eeb2e1a8e688dfec753e8965d0e5aeb119e638 for Ticket #481
    "expand nested posix groups" introduced these compiler warnings.
    
    1) posix-grou-func.c
    . added missing format strings "%s" in searchUid.
    . added a function declaration hasObjectClass.
    . eliminated an unused variable uid_dn_value.
    2) posix-group-task.c
    . included "slapi-private.h" for filter_escaped_value.
    (cherry picked from commit 56ebbb20fa9f8d1add75075fdf421f53ed5348f1)