Restore cwd if debugger setUp() fails (to avoid breaking later tests).

Cython/Debugger/Tests/TestLibCython.py

@@ -90,6 +90,7 @@ class DebuggerTestCase(unittest.TestCase):
         self.cfuncs_destfile = os.path.join(self.tempdir, 'cfuncs')
 
         self.cwd = os.getcwd()
+        try:
             os.chdir(self.tempdir)
 
             shutil.copy(codefile, self.destfile)
@@ -145,6 +146,10 @@ class DebuggerTestCase(unittest.TestCase):
                 # cmdclass=dict(build_ext=Cython.Distutils.build_ext)
             # )
 
+        except:
+            os.chdir(self.cwd)
+            raise
+
     def tearDown(self):
         if not test_gdb():
             return