======Synopsis:======
[[set]] banner_expand [on|off|toggle]

======Description:======
If ON: The value of [[set banner]] is run through expando-substution every 
time it is used.
If OFF: The value of [[set banner]] is taken as a literal string.

======Practical:======
This is useful if you like to display the current time ($Z) in your banner.

======Example:======
/set banner_expand ON
/set banner $Z %%***%%

  9:00PM *** CTCP PING from MrFoo detected