Make the test suite print a summary of XFAIL tests, as well as the
summaries of skipped and failed (including XPASS) tests that it already
prints.

* build/run_tests.py
  (TestHarness.run): Print a summary of XFAIL results as well as others.
    Tweak the grammar of the summary messages.

Index: build/run_tests.py
===================================================================
--- build/run_tests.py	(revision 32894)
+++ build/run_tests.py	(working copy)
@@ -70,10 +70,15 @@
       cnt += 1
     self._open_log('r')
     log_lines = self.log.readlines()
+    # Print summaries from least interesting to most interesting.
     skipped = filter(lambda x: x[:6] == 'SKIP: ', log_lines)
     if skipped:
       print 'At least one test was SKIPPED, checking ' + self.logfile
       map(sys.stdout.write, skipped)
+    xfailed = filter(lambda x: x[:6] == 'XFAIL:', log_lines)
+    if xfailed:
+      print 'At least one test XFAILED, checking ' + self.logfile
+      map(sys.stdout.write, xfailed)
     if failed:
       print 'At least one test FAILED, checking ' + self.logfile
       map(sys.stdout.write, filter(lambda x: x[:6] in ('FAIL: ', 'XPASS:'),