Remove unique constraints for custom_fields on fields (object_id, object_type, field_name) and implement the check on uniqueness in the java code so as to support adding and removing multiple times a cutom field for the same object and with the same key
Update oss version to get latest api version
[maven-release-plugin] prepare release killbill-0.8.8
[maven-release-plugin] prepare for next development iteration
Merge remote-tracking branch 'origin/master' into bitcoin

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>

Conflicts:
	pom.xml
	util/src/main/java/com/ning/billing/util/customfield/api/DefaultCustomFieldUserApi.java