edx/XBlock — pull request #57 by peter-fogg (2013-08-08 18:13:05+00:00)
Title: Prevent mutable fields from incorrectly becoming dirty.

Fixes a bug in Studio by allowing us to reliably tell whether or not a
field has been explicitly set. Previously, because accessing a mutable
field marked it dirty, it was impossible to tell if a field was
actually modified by a course author.