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_resultlog.py

@@ -1,7 +1,7 @@
 import py
 import os
-from py.__.test.plugin.pytest_resultlog import generic_path, ResultLog
-from py.__.test.collect import Node, Item, FSCollector
+from _py.test.plugin.pytest_resultlog import generic_path, ResultLog
+from _py.test.collect import Node, Item, FSCollector
 
 def test_generic_path():
     p1 = Node('a')