kind=defined
names=make_expires
visibility=public

--- make_expires(sec = nil)

Returns an expiry Time based on +sec+ which can be one of:

Numeric: +sec+ seconds into the future

+true+:  the expiry time is the start of 1970 (i.e. expired)

+nil+:   it is Tue Jan 19 03:14:07 GMT Standard Time 2038 (i.e.
         when UNIX clocks will die)

