[plt-scheme] bugs in snapshot mz-3.99.0.10

hello,

moving to 3.99 i found some bugs in snapshot mz-3.99.0.10
downloaded Mon Feb 11 2008

1.

> (require (lib "lazy.ss" "srfi" "45"))
> (s:force (s:delay '()))

gives the error:
car: expects argument of type <pair>; given {#f . #<procedure>}

changed car -> mcar on line 33 in collects/srfi/45/lazy.ss


2.

sleep: expects argument of type <non-negative real number>; given #f

 === context ===
/usr/local/mz-3.99.0.10/collects/scheme/sandbox.ss:218:21

(call-with-limits sec mb thunk)
;; sec -> #f

the doc says the parameter can be false, so i wrapped a (when sec ...)
around the body of the timer thread thunk.


----

the move to immutable pairs seems to work pretty well for my largest plt 
scheme project (forth compiler http://zwizwa.h1x.com/brood, about 12k lines)

was fairly straigthforward:
 * a couple of reverse! -> reverse
 * explicit use of mutable pairs in 1 isolated file