Make uncaught exceptions in teaching languages pop up test-engine display.

... so as to catch any test-case failures or signature violations that
may have occurred.

collects/deinprogramm/deinprogramm-langs.rkt

@@ -191,7 +191,12 @@
 
 		 ;; hack: the test-engine code knows about the test~object name; we do, too
 		 (namespace-set-variable-value! 'test~object (build-test-engine))
-		 ;; record test-case failures with the test engine
+		 (uncaught-exception-handler
+		  (let ((previous (uncaught-exception-handler)))
+		    (lambda (exc)
+		      (display-results)
+		      (previous exc))))
+		 ;; record signature violations with the test engine
 		 (signature-violation-proc
 		  (lambda (obj signature message blame)
 		    (cond

collects/lang/htdp-langs.rkt

@@ -33,7 +33,8 @@
          
          (only-in test-engine/scheme-gui make-formatter)
          (only-in test-engine/scheme-tests 
-		  scheme-test-data error-handler test-format test-execute build-test-engine)
+		  scheme-test-data error-handler test-format test-execute display-results
+		  build-test-engine)
          (lib "test-engine/test-display.scm")
 	 deinprogramm/signature/signature
          )
@@ -155,7 +156,12 @@
                  (namespace-require scheme-signature-module-name)
 		 ;; hack: the test-engine code knows about the test~object name; we do, too
 		 (namespace-set-variable-value! 'test~object (build-test-engine))
-		 ;; record test-case failures with the test engine
+		 (uncaught-exception-handler
+		  (let ((previous (uncaught-exception-handler)))
+		    (lambda (exc)
+		      (display-results)
+		      (previous exc))))
+		 ;; record signature violations with the test engine
 		 (signature-violation-proc
 		  (lambda (obj signature message blame)
 		    (cond