sleep of non-positive duration now returns immediately

LOG

@@ -2146,3 +2146,5 @@
     c/expeditor.c, c/externs.h, c/prim5.c, c/scheme.c, c/stats.c
 - fix signature of generate-temporaries
     primdata.ss primvars.ss
+- sleep of negative durations now returns immediately
+    7.ss

release_notes/release_notes.stex

@@ -1906,6 +1906,12 @@ in fasl files does not generally make sense.
 %-----------------------------------------------------------------------------
 \section{Bug Fixes}\label{section:bugfixes}
 
+\subsection{\protect\scheme{sleep} with negative duration (9.5.5)}
+
+Prior to this release, \scheme{sleep} of a negative duration would
+result in an infinite pause in Windows. Now \scheme{sleep} returns
+immediately on all platforms when given a negative duration.
+
 \subsection{Flonum \protect\scheme{remainder} and \protect\scheme{modulo} (9.5.5)}
 
 The \scheme{remainder} and \scheme{modulo} functions could produce

s/7.ss

@@ -699,7 +699,9 @@
     (lambda (t)
       (unless (and (time? t) (eq? (time-type t) 'time-duration))
         ($oops who "~s is not a time record of type time-duration" t))
-      (fp (time-second t) (time-nanosecond t)))))
+      (let ([s (time-second t)])
+        (when (>= s 0)
+          (fp s (time-nanosecond t)))))))
 
 (define $scheme-greeting
   (lambda ()