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/process/test_cmdexec.py

@@ -30,7 +30,7 @@ class Test_exec_cmd:
             assert e.err or e.out
 
 def test_cmdexec_selection():
-    from py.__.process import cmdexec 
+    from _py.process import cmdexec 
     if py.std.sys.platform == "win32":
         assert py.process.cmdexec == cmdexec.win32_exec_cmd
     elif hasattr(py.std.sys, 'pypy') or hasattr(py.std.sys, 'pypy_objspaceclass'):