Make sure port locks get released after I/O errors.

scheme/rts-packages.scm

@@ -84,7 +84,7 @@
 	interrupts      ; {en|dis}able-interrupts!
 	number-i/o      ; number->string for debugging
 	exceptions      ; wrong-number-of-args stuff
-	handle)		; report-errors-as-warnings
+	handle)		; report-errors-as-warnings with-handler
   (files (rts port)
 	 (rts current-port))
   (optimize auto-integrate))

scheme/rts/port.scm

@@ -206,7 +206,14 @@
 	   (begin
 	     (obtain-port-lock ?port)         ; lock the port
 	     (if (open-port? ?port)           ; check that it's open
-		 (let ((value ?body))         ; do the work
+		 (let ((value		      ; do the work
+			(with-handler
+			 (lambda (condition punt)
+
+			   (release-port-lock ?port)
+			   (punt))
+			 (lambda ()
+			   ?body))))
 		   (release-port-lock ?port)  ; release the lock
 		   value)                     ; return
 		 (begin