Tests illustrating the problem with multiple identical from future statements added to single file.
Logging diagnostics which demonstrate roots of the problem (break
on no names)
More tests, going to check possible fix on multiple-files run.
Looks like this line was responsible for the problem.
For some reason this file crashes with

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/home/marcink/DEV_git/python/python-modernize/tests/test_future_behaviour.py", line 92, in test_problematic_file
    _check_on_input(prb_content)
  File "/home/marcink/DEV_git/python/python-modernize/tests/test_future_behaviour.py", line 49, in _check_on_input
    modernize_main(extra_flags + ["-w", test_input_name])
  File "/home/marcink/DEV_git/python/python-modernize/libmodernize/main.py", line 117, in main
    options.processes)
  File "/usr/lib64/python2.7/lib2to3/refactor.py", line 706, in refactor
    items, write, doctests_only)
  File "/usr/lib64/python2.7/lib2to3/refactor.py", line 301, in refactor
    self.refactor_file(dir_or_file, write, doctests_only)
  File "/usr/lib64/python2.7/lib2to3/refactor.py", line 747, in refactor_file
    *args, **kwargs)
  File "/usr/lib64/python2.7/lib2to3/refactor.py", line 354, in refactor_file
    tree = self.refactor_string(input, filename)
  File "/usr/lib64/python2.7/lib2to3/refactor.py", line 386, in refactor_string
    self.refactor_tree(tree, name)
  File "/usr/lib64/python2.7/lib2to3/refactor.py", line 460, in refactor_tree
    new = fixer.transform(node, results)
  File "/home/marcink/DEV_git/python/python-modernize/libmodernize/fixes/fix_print.py", line 73, in transform
    add_future(node, u'print_function')
  File "/home/marcink/DEV_git/python/python-modernize/libmodernize/__init__.py", line 51, in add_future
    names = check_future_import(node)
  File "/home/marcink/DEV_git/python/python-modernize/libmodernize/__init__.py", line 18, in check_future_import
    node.children[1].value == u'__future__'):
AttributeError: 'Node' object has no attribute 'value'
This still fails
Simplified test to the extreme (likely)
Resolved second crash. Debugging showed, that in this very case (from
a.b.c. import d) node.children[1] was itself a node with children (and
without value)
Merge branch 'multiple-futures-fix' of https://github.com/Mekk/python-modernize