Bump version to 1.7.2
DigitalObject.changed? should be false after successful save
accomodate Fedora bug re: w3c date representations
Merge pull request #71 from barmintor/rubydora-70

DigitalObject.changed? should be false after successful save
rubydora-72: Make use of ds profiles on create and update
- modify ds profiles in-place after save
- cache resulting dsCreateDate as lastModifiedDate on DigitalObject
- refactor ds saves into method in DigitalObject
Merge pull request #73 from barmintor/rubydora-72

rubydora-72: Make use of ds profiles on create and update
Prepare for version 1.7.3
Ensure datastream timestamp is valid before using it.
A datastream may not be saved (e.g. callback returns false) in which
case its dsCreateDate is nil.  Don't try to parse a time out of the nil
value.
Merge pull request #74 from projecthydra/no_update_nil_times

Ensure datastream timestamp is valid before using it.
Prepare for 1.7.4