Synopsis:
   $tdiff(<seconds>)

Technical:
   * If the argument is omitted, the empty string is returned
   * The argument is taken to be the number of seconds (floating point
     is permitted) between two timed events.
   * This function returns the number of elapsed seconds in the following
     format:
		<integer> is taken as everything before a '.' in <seconds>.
		<after> is taken as everything after a '.' in <seconds>.
		<tsec> is <integer> % 60;
		<tmin> is (<integer> / 60) % 60;
		<thour> is (<integer> / 3600) % 24;
		<tday> is (<integer> / 86400);

	If <tday> is 0, then nothing
	If <tday> is 1, then "1 day "
	Otherwise, then "<tday> days "
    plus
	If <thour> is 0, then nothing
	If <thour> is 1, then "1 hour "
	Otherwise, then "<thour> hours "
    plus
	If <tmin> is 0, then nothing
	If <tmin> is 1, then "1 minute "
	Otherwise, then "<tmin> minutes "
    plus
	If <tsec> is not zero or all of <tday>, <thour>, <tmin> are zero,
	    or <after> exists, then 
		If <after> exists, then <sec> is "<tsec>.<after>"
			return value is "<sec> seconds"
		If <tsec> is 1, then "<sec> second"
		Otherwise, then "<sec> seconds"

    * If a trailing space exists at the end of the string, remove it.
    * Negative numbers are acceptable and will yield negative results.

Practical:
   This function is useful for showing how much time has elapsed since a
   particular event.  For instance, it can convert your idle time from the
   number of seconds to a more readable form.

Returns:
   A human readable string representing some elapsed time.

Cost:
   This function has a relative cost of ... deltas.  (One inward argument,
	6 floating point operations, a printf operation, and a return
	value)

History:
   This function first appeared in ircII.

Examples:
   $tdiff(248576)      returns "2 days 21 hours 2 minutes 56 seconds"
   $tdiff(-248576)     returns "-2 days -21 hours -2 minutes -56 seconds"

