Fix `use constant' usage for MSYS Perl 5.6.0. * automake.in (QUEUE_MESSAGE, QUEUE_CONF_FILE, QUEUE_LOCATION) (QUEUE_STRING): Define using one `use constant' each; as perl 5.6.0 (on MSYS) does not understand `use constant { ... }'. * THANKS: Update. Report by Peter Rosin. Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>