[plt-scheme] Bug in url.ss? Parameter wrapped with contract

Hi all,

The current-proxy-servers parameter defined in url-unit.ss is wrapped
with a contract in url.ss.  This means that parameterize complains if
you pass it current-proxy-servers:

> (parameterize ([current-proxy-servers '(foo)]) (+ 1 2))
parameterize: expects type <parameter> as 2nd argument, given:
#<procedure:current-proxy-servers>; other arguments were:
#<parameterization> (foo)

[Yeah I know '(foo) doesn't meet the contract]

Is this intentional?  If not, I guess I'll fix it.

N.