fix issue78 - now python-level teardown functions are now called even if the setup failed.

Important detail: if the setup raises a Skipped exception, teardown will not be called.  This helps
to avoid breaking setup_module/class that performs a skip - it would otherwise internally
be considered as a "successful" setup in order to have teardown called later.  I guess
it also makes sense to treat Skip specially because it is unlikely a teardown should be
called if a Skip was raised on setup.

In any case, failing setups and teardowns will be reported separately.

--HG--
branch : trunk

py/_plugin/pytest_runner.py

@@ -249,5 +249,9 @@ class SetupState(object):
                 break 
             self._pop_and_teardown()
         for col in needed_collectors[len(self.stack):]: 
-            col.setup() 
             self.stack.append(col) 
+            try:
+                col.setup() 
+            except Skipped:
+                self.stack.pop()
+                raise