Add add_bundle() support
Check for pre-existing bundle with same ID before adding one
Merge branch 'master' of github.com:millr/prov into millr-master

Conflicts:
	prov/persistence/models.py

Signed-off-by: Trung Dong Huynh <trungdong@donggiang.com>
Changed: check for the existence of the bundle's id
Add support for adding bundles to pre-existing documents
Assume a valid identifier has been assigned to bundle when appending one
Check for pre-existing bundle with same ID before adding one
Changed: check for the existence of the bundle's id
Add support for adding bundles to pre-existing documents
Assume a valid identifier has been assigned to bundle when appending one
Merge branch 'millr-master' of https://github.com/trungdong/prov into millr-master
Fix provn representation of bundles' namespaces

Previously only root document namespaces would be shown. Now namespaces are also shown in bundles.
Fix add_bundle to add a record entry and verify integrity of add
Merge branch 'millr-master'

Conflicts:
	prov/model/__init__.py

Signed-off-by: Trung Dong Huynh <trungdong@donggiang.com>