Implements Scheme Request For Implementation (SRFI) as
described at http://srfi.schemers.org/
Syntax: Each <clause> should be of the form(<feature> <expression1> ...)
where <feature> is a boolean expression composed of symbols and `and', `or', and `not' of boolean expressions. The last <clause> may be an “else clause,” which has the form(else <expression1> <expression2> ...).
The first clause whose feature expression is satisfied is expanded. If no feature expression is satisfied and there is no else clause, an error is signaled.
cond-expandis an extension of SRFI-0, http://srfi.schemers.org/srfi-0/srfi-0.html.
(define error slib:error)