Release 1.6.0beta21.
Release 1.6.0beta21.

jscinoz/assetgraph,papandreou/assetgraph,jscinoz/assetgraph,slang800/assetgraph,slang800/assetgraph,papandreou/assetgraph,assetgraph/assetgraph,papandreou/assetgraph,jscinoz/assetgraph