Small change that guards against flushable read-sequence in earlier

versions of CMU CL, as well as guarding against short reads by
read-sequence on socket streams, though my understanding of the
standard seems to imply that read-sequence can only return prematurely
on EOF.  But this way we shouldn't have any problems either way.

src/main/messages.cl

@@ -343,7 +343,9 @@ used to call `reinitialize-instance'."))
 	 (stream (request-stream request)))
     (when length
       (let ((buffer (make-string length)))
-	(read-sequence buffer stream)
+	(do ((start 0))
+	    ((>= (incf start (read-sequence buffer stream :start start))
+		 length)))
 	(make-instance 'string-entity :content-length length
 		       :content-type (cdr (assoc "content-type" headers
 						 :test #'string-equal))