Check for features exclusions before adding new dependency

Problem/Motivation

The features integration in this module checks for other modules that are implementing same subfields of a field_group, and tries to add that feature or module as a dependency. This works quite well in most cases, however it does not respect exclusions set by the feature itself.

Note: this problem seems to happen to us only when we use the drush command "drush features-update", updating modules through the features UI seems to cause no problems.

Example:
In the .info file of feature_a (enabled) we have the following line:
features_exclude[dependencies][feature_b] = feature_b

When updating Feature A through the Features UI management screen, the excluded dependency will not get added by field_group. However when updating the features through drush (drush features-update [name]), field_group will add feature_b as a dependency despite it being excluded.

Proposed resolution

Add a check in field_group.features.inc to only add a dependency when there is NO exclusion defined. See attached patch.