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

_py/test/plugin/pytest_hooklog.py

@@ -0,0 +1,31 @@
+""" log invocations of extension hooks to a file. """ 
+import py
+
+def pytest_addoption(parser):
+    parser.addoption("--hooklog", dest="hooklog", default=None, 
+        help="write hook calls to the given file.")
+
+def pytest_configure(config):
+    hooklog = config.getvalue("hooklog")
+    if hooklog:
+        config._hooklogfile = open(hooklog, 'w')
+        config._hooklog_oldperformcall = config.hook._performcall
+        config.hook._performcall = (lambda name, multicall: 
+            logged_call(name=name, multicall=multicall, config=config))
+
+def logged_call(name, multicall, config):
+    f = config._hooklogfile
+    f.write("%s(**%s)\n" % (name, multicall.kwargs))
+    try:
+        res = config._hooklog_oldperformcall(name=name, multicall=multicall)
+    except:
+        f.write("-> exception")
+        raise
+    f.write("-> %r" % (res,))
+    return res
+
+def pytest_unconfigure(config):
+    try:
+        del config.hook.__dict__['_performcall'] 
+    except KeyError:
+        pass