rewrote the initpkg mechanism and moved py lib implementation files to

_py/...  with py/__init__.py containing pointers into them

The new apipkg is only around 70 lines of code and allows
us to get rid of the infamous "py.__." by regular non-magical
"_py." imports. It is also available as a separately installable
package, see http://bitbucket.org/hpk42/apipkg

--HG--
branch : trunk

testing/pytest/plugin/test_pytest_doctest.py

@@ -1,4 +1,4 @@
-from py.__.test.plugin.pytest_doctest import DoctestModule, DoctestTextfile
+from _py.test.plugin.pytest_doctest import DoctestModule, DoctestTextfile
 
 class TestDoctests:
  
@@ -33,7 +33,7 @@ class TestDoctests:
         reprec.assertoutcome(failed=1)
 
     def test_doctest_unexpected_exception(self, testdir):
-        from py.__.test.outcome import Failed 
+        from _py.test.outcome import Failed 
 
         p = testdir.maketxtfile("""
             >>> i = 0