Add 'set_image_location' policy option

Gives operators the option to prevent references to 'external' image data.

Addresses bug 1153613.

Change-Id: I68aac9039eed0f70ed3b893f5c51838a70d290ae
remove deprecated assert_unicode sqlalchemy attribute

Removing this enables use with sqlalchemy 0.8.0
The deprecation is described upstream at:
http://docs.sqlalchemy.org/en/latest/changelog/changelog_08.html#change-ad44af79c886d1bb283042deb64f9cbe

Change-Id: Ia34b38245c6abe1ddb4162eee89459a7130deacb
Merge "Add 'set_image_location' policy option"
Merge "remove deprecated assert_unicode sqlalchemy attribute"