add clean target
Change ac warn to debug log
Merge branch 'develop' of github.com:AKSW/Erfurt into develop
Enhance performance by accessing model only if needed

- model is only access, when namespaces are not yet fetched, which saves some
  SPARQL queries
Use faster way to add items to array
Enhance performance by using graphUri directly

- model instance was only used to obtain the graph URI, which leads to some
  unneccesary  SPARQL queries
Fix regression in getNamespacesForGraph
correct doc block for two prefix functions
add methdo getReadableGraphsUsingResource to Store
adjust year in doc block
Fix strict standard conformance
always set str to lower case on prefix (and coding standard)
deb changes for 1.4
Merge tag 'v1.4'

v1.4