UPDATE_CONFIG: Tell the daemon to update config of some key.
Any user can really request that values are
re-read but the daemon caches the last date
of the config file so a user can't actually
change any values unless they can write the
config file.
Supported keys:
security/AllowRoot (2.3.90.2)
security/AllowRemoteRoot (2.3.90.2)
security/AllowRemoteAutoLogin (2.3.90.2)
security/RetryDelay (2.3.90.2)
security/DisallowTCP (2.4.2.0)
daemon/Greeter (2.3.90.2)
daemon/RemoteGreeter (2.3.90.2)
xdmcp/Enable (2.3.90.2)
xdmcp/Port (2.3.90.2)
xdmcp/PARAMETERS (2.3.90.2) (pseudokey, all the parameters)
xdmcp/MaxPending
xdmcp/MaxSessions
xdmcp/MaxWait
xdmcp/DisplaysPerHost
xdmcp/HonorIndirect
xdmcp/MaxPendingIndirect
xdmcp/MaxWaitIndirect
xdmcp/PingIntervalSeconds (only affects new connections)
daemon/TimedLogin (2.3.90.3)
daemon/TimedLoginEnable (2.3.90.3)
daemon/TimedLoginDelay (2.3.90.3)
greeter/SystemMenu (2.3.90.3)
greeter/ConfigAvailable (2.3.90.3)
greeter/ChooserButton (2.4.2.0)
greeter/SoundOnLoginFile (2.5.90.0)
daemon/AddGtkModules (2.5.90.0)
daemon/GtkModulesList (2.5.90.0)
Supported since: 2.3.90.2
Arguments:  <key>
<key> is just the base part of the key such as
"security/AllowRemoteRoot"
Answers:
OK
ERROR <err number> <english error description>
0 = Not implemented
50 = Unsupported key
200 = Too many messages
999 = Unknown error
