Refs #188 - Items pay attention to their current date values when possibly changing their date ranges due to new sub-items.
Refs #188 - Overhauling how and when all four kinds of object-table-cached derived fields are calculated.
Refs #188 - Grep out undefined ancestors
Refs #188 - Avoiding adding spurious "update" log messages during derived-field-setting.
Refs #188 - Adding some commentary.
Refs #188 - Tossing out references to the old way of defining restriction summaries. Finessing which objects, exactly, get the ancestor-editing treatment.
Refs #188 - Adds new columns to the item table.
Refs #188 - Accounting for the fact that an object's descendants' latest date might be found in the item_date_from column as well as item_date_to.
Refs #188 - Updating a couple of tests to work with new item-date columns.
Merge branch 'master' into 188-bad_date_range_handling
Merge pull request #28 from TuftsUniversity/188-bad_date_range_handling

FIXES 188 bad date range handling