When iterating over the names imported in a future statement, ignore the commas in the concrete syntax; checking those causes a segfault.
When iterating over the names imported in a future statement, ignore the
commas in the concrete syntax; checking those causes a segfault.

This fixes SF bug #407394.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator