Refs #5538 - Added regression test
Fixes #5538 - Adds Additional columns filtering in AttributeLoader
Refs #5543 - Regression test
Fixes #5543 - Adds ElggEntity::loadAdditionalColumns that loads additional select columns into volatile data with prefix row:
Refs #5544 - Regression test
Fixes #5544 - Allow new data to be injected into entity if query performed
fixed line endings and replaced calls to elgg_get_metadata_cache()
changed key name to start with 'select' rather than row - also some general cleanup
Merge pull request #5676 from cash/pr-5548

Adds support for additional columns in selects