run-tests: report timeouts in a less alarming fashion

Rather than report timed-out tests like this:

 ERROR: test-convert-svn-sink.t output changed
 !

..simply put a 't' rather than a '.' in the stream.

tests/run-tests.py

@@ -1273,10 +1273,13 b' class TestResult(unittest._TextTestResul'
             self.stop()
         else:
             with iolock:
+                if reason == "timed out":
+                    self.stream.write('t')
+                else:
                 if not self._options.nodiff:
                     self.stream.write('\nERROR: %s output changed\n' % test)
+                    self.stream.write('!')
 
-                self.stream.write('!')
                 self.stream.flush()
 
     def addSuccess(self, test):

tests/test-run-tests.t

@@ -412,9 +412,7 b' timeouts'
   > cat test-timeout.t >> test-slow-timeout.t
   $ run-tests.py --with-hg=`which hg` --timeout=1 --slowtimeout=3 \
   > test-timeout.t test-slow-timeout.t
-  s
-  ERROR: test-timeout.t output changed
-  !
+  st
   Skipped test-slow-timeout.t: skipped
   Failed test-timeout.t: timed out
   # Ran 1 tests, 1 skipped, 0 warned, 1 failed.
@@ -422,9 +420,7 b' timeouts'
   [1]
   $ run-tests.py --with-hg=`which hg` --timeout=1 --slowtimeout=3 \
   > test-timeout.t test-slow-timeout.t --allow-slow-tests
-  .
-  ERROR: test-timeout.t output changed
-  !
+  .t
   Failed test-timeout.t: timed out
   # Ran 2 tests, 0 skipped, 0 warned, 1 failed.
   python hash seed: * (glob)