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.
(binary:application/octet-stream)