sandbox/dan2: merging changes from trunk; some further small code-level...

sandbox/dan2: merging changes from trunk; some further small code-level optimizations to determinization code (which I just realized were done in sandbox/dan2; I'll now merge those back to trunk.

git-svn-id: https://svn.code.sf.net/p/kaldi/code/sandbox/dan2@3087 5e6a8d80-dfce-4ca6-a32a-6e07a63d50c8