simplify pluginmanager, move plugin validation code to plugin, remove unused code

--HG--
branch : trunk

testing/plugin/test_pytest_helpconfig.py

@@ -1,4 +1,5 @@
 import py, os
+from py.plugin.pytest_helpconfig import collectattr
 
 def test_version(testdir):
     assert py.version == py.__version__ 
@@ -16,3 +17,15 @@ def test_helpconfig(testdir):
         "*cmdline*conftest*ENV*",
     ])
 
+def test_collectattr():
+    class A:
+        def pytest_hello(self):
+            pass
+    class B(A):
+        def pytest_world(self):
+            pass
+    methods = py.builtin.sorted(collectattr(B))
+    assert list(methods) == ['pytest_hello', 'pytest_world']
+    methods = py.builtin.sorted(collectattr(B()))
+    assert list(methods) == ['pytest_hello', 'pytest_world']
+