Possible infinite loop in _features_export_maximize_dependencies

Hi there,

just found a possible issue in _features_export_maximize_dependencies().
The method uses recursion to detect all dependencies of the modules to export.
But there's no infinite loop protection.
I've just updated to Drupal 7 CVS today and there's a circular module dependency introduced. (field->field_sql_storage, field_sql_storage->field)
I don't think it's intentionally introduced but it's there, and features should be able to handle this.

My patch prevents the function from resolving already known dependencies. This by using a static variable which is cleaned on every first call of the function.
The recursion is still in place but shouldn't lead to a infinite loop.

Cheers,
Peter