GTTF: Print much better error message for dependency cycles.

test/small/gyptest-small.py

 #!/usr/bin/env python
 
 # Copyright (c) 2012 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Runs small tests.
 """
 
@@ skipping 12 matching lines @@
 sys.path.append(os.path.join(test._cwd, 'pylib'))
 
 # Add new test suites here.
 files_to_test = [
     'pylib/gyp/MSVSSettings_test.py',
     'pylib/gyp/easy_xml_test.py',
     'pylib/gyp/generator/msvs_test.py',
     'pylib/gyp/generator/ninja_test.py',
     'pylib/gyp/generator/xcode_test.py',
     'pylib/gyp/common_test.py',
+    'pylib/gyp/input_test.py',
 ]
 
 # Collect all the suites from the above files.
 suites = []
 for filename in files_to_test:
   # Carve the module name out of the path.
   name = os.path.splitext(os.path.split(filename)[1])[0]
   # Find the complete module path.
   full_filename = os.path.join(test._cwd, filename)
   # Load the module.
   module = imp.load_source(name, full_filename)
   # Add it to the list of test suites.
   suites.append(unittest.defaultTestLoader.loadTestsFromModule(module))
 # Create combined suite.
 all_tests = unittest.TestSuite(suites)
 
 # Run all the tests.
 result = unittest.TextTestRunner(verbosity=2).run(all_tests)
 if result.failures or result.errors:
   test.fail_test()
 
 test.pass_test()