make py lib a self-contained directory again

- move and merge _py/ bits back to py/
- fixes all around

--HG--
branch : trunk

py/impl/std.py

@@ -0,0 +1,18 @@
+import sys
+
+class Std(object):
+    """ makes top-level python modules available as an attribute, 
+        importing them on first access. 
+    """ 
+
+    def __init__(self):
+        self.__dict__ = sys.modules
+
+    def __getattr__(self, name):
+        try:
+            m = __import__(name)
+        except ImportError:
+            raise AttributeError("py.std: could not import %s" % name)
+        return m
+
+std = Std()