cli: decode all cli arguments, assuming that they are utf-8 encoded

Also encode all args to urllib as utf-8 because urllib doesn't handle unicode objects.
I'm not sure if it is appropriate to *assume* utf-8 encoding of cli args.  Perhaps the Right thing to do is to detect the platform encoding.  Any ideas?
This patch is mostly due to François Deppierraz.

src/allmydata/scripts/common.py

@@ -129,4 +129,4 @@ def get_alias(aliases, path, default):
 
 def escape_path(path):
     segments = path.split("/")
-    return "/".join([urllib.quote(s) for s in segments])
+    return "/".join([urllib.quote(s.encode('utf-8')) for s in segments])

src/allmydata/scripts/runner.py

@@ -33,6 +33,12 @@ def runner(argv,
            stdin=sys.stdin, stdout=sys.stdout, stderr=sys.stderr,
            install_node_control=True, additional_commands=None):
 
+    # Convert arguments to unicode
+    new_argv = []
+    for arg in argv:
+      new_argv.append(arg.decode('utf-8'))
+    argv = new_argv
+
     config = Options()
     if install_node_control:
         config.subCommands.extend(startstop_node.subCommands)