[PATCH 1 of 2] import-checker: increase portability for python 2.6.x

[FUJIWARA Katsunori]

# HG changeset patch
# User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
# Date 1466270109 -32400
#      Sun Jun 19 02:15:09 2016 +0900
# Node ID 04da1198949bcd8c1d1fd6675816eacfdc2f3dcf
# Parent  4e6e280e238fa885df9e0e600dc5915a71c8a37a
import-checker: increase portability for python 2.6.x

Before this patch, fromlocalfunc() assumes that "module" attribute of
ast.ImportFrom is None for "from . import a", and Python 2.7.x
satisfies this assumption.

On the other hand, with Python 2.6.x, "module" attribute of
ast.ImportFrom is an empty string for "from . import a", and this
causes failure of test-check-module-imports.t.

diff --git a/contrib/import-checker.py b/contrib/import-checker.py
--- a/contrib/import-checker.py
+++ b/contrib/import-checker.py
@@ -141,8 +141,8 @@ def fromlocalfunc(modulename, localmods)
     if prefix:
         prefix += '.'
     def fromlocal(name, level=0):
-        # name is None when relative imports are used.
-        if name is None:
+        # name is false value when relative imports are used.
+        if not name:
             # If relative imports are used, level must not be absolute.
             assert level > 0
             candidates = ['.'.join(modulename.split('.')[:-level])]