Declare types for BasedirOptions. Fixes several errors.

src/allmydata/scripts/common.py

@@ -4,6 +4,11 @@ import os, sys, urllib, textwrap
 import codecs
 from os.path import join
 
+try:
+    from typing import Optional, Sequence, List
+except ImportError:
+    pass
+
 # Python 2 compatibility
 from future.utils import PY2
 if PY2:
@@ -64,7 +69,7 @@ class BasedirOptions(BaseOptions):
     optParameters = [
         ["basedir", "C", None, "Specify which Tahoe base directory should be used. [default: %s]"
          % quote_local_unicode_path(_default_nodedir)],
-    ]
+    ]  # type: List[Sequence[Optional[str]]]
 
     def parseArgs(self, basedir=None):
         # This finds the node-directory option correctly even if we are in a subcommand.