Switch off signal dumper when testing is completed.

Previously, if the signal dumper was switched on with the -vs
command-line switch, it would never be switched off again.

Change-Id: I192e188010471525723fad0844ff33e9482128ea
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>

src/testlib/qtestcase.cpp

@@ -1991,6 +1991,9 @@ int QTest::qExec(QObject *testObject, int argc, char **argv)
 #endif
 
     currentTestObject = 0;
+
+    QSignalDumper::endDump();
+
 #ifdef Q_WS_MAC
      if (macNeedsActivate) {
          IOPMAssertionRelease(powerID);