demo: add wrapper to easily monkey-patch re6st

Also:
- use '/usr/bin/env python' to easily use a Python interpreter different than
  /usr/bin/python
- demo must be run by root so "dont_write_bytecode" to avoid having *.pyc files
  owned by root in the working copy

demo/demo

@@ -161,8 +161,8 @@ if 1:
         " -subj /CN=re6st.example.com/emailAddress=re6st@example.com"
         " -set_serial 0x120010db80042 -days %u" % CA_DAYS, shell=True)
     db_path = 'registry/registry.db'
-    registry.screen('../re6st-registry @registry/re6st-registry.conf --db %s'
-        ' --mailhost %s -v%u --control-socket registry/babeld.socket'
+    registry.screen('./py re6st-registry @registry/re6st-registry.conf'
+        ' --db %s --mailhost %s -v%u --control-socket registry/babeld.socket'
         % (db_path, os.path.abspath('mbox'), VERBOSE))
     registry_url = 'http://%s/' % REGISTRY
     registry.Popen(('python', '-c', """if 1:
@@ -183,7 +183,7 @@ if 1:
             if not os.path.exists(dh_path):
                 os.symlink('../dh2048.pem', dh_path)
             email = node.name + '@example.com'
-            p = node.Popen(('../../re6st-conf', '--registry', registry,
+            p = node.Popen(('../py', 're6st-conf', '--registry', registry,
                 '--email', email), stdin=subprocess.PIPE, cwd=folder)
             token = None
             while not token:
@@ -196,7 +196,7 @@ if 1:
             p.communicate(str(token[0]))
             os.remove(dh_path)
             os.remove(folder + '/ca.crt')
-        node.screen('../re6stnet @%s/re6stnet.conf -v%u --registry %s'
+        node.screen('./py re6stnet @%s/re6stnet.conf -v%u --registry %s'
                     ' --control-socket %s/babeld.socket'
                     ' %s' % (folder, VERBOSE, registry, folder, args))
     re6stnet(registry, 'registry', '--ip ' + REGISTRY, registry='http://localhost/')

demo/py

+#!/usr/bin/env python
+def __file__():
+    import argparse, os, sys
+    sys.dont_write_bytecode = True
+    sys.path[0] = os.path.dirname(sys.path[0])
+    from argparse import ArgumentParser
+    _parse_args = ArgumentParser.parse_args
+    ArgumentParser.parse_args = lambda self: _parse_args(self, sys.argv[2:])
+
+    return os.path.join(sys.path[0], sys.argv[1])
+__file__ = __file__()
+execfile(__file__)