The field_bundle_settings variable stores administratively defined settings about each bundle, including its view modes and extra fields.
Previously, settings for all bundles across all entity types were stored in one variable, field_bundle_settings. Now each bundle's settings are stored in a separate variable, following the pattern field_bundle_settings_ENTITYTYPE__BUNDLENAME.
For example, the bundle settings for the Article node type would be stored in a variable called field_bundle_settings_node__article.
Any module retrieving this data would continue to use field_bundle_settings(), which was not changed.
This would only affect modules that directly accessed this variable instead of using the field_bundle_settings() function, or any module that exported the variable by using the Strongarm module.
