implement GetEnteringArcs.

[csukuangfj]

// CHECK(CheckProperties(fsa, KTopSorted));

is currently disabled.

Should we use glog or implement our own glog like functions ?

[danpovey]

Fantastic!
I'm OK to include glog, depending what the others think...

[csukuangfj]

@qindazhu @galv
what do you think about glog?

[qindazhu]

I'm ok with glog.

[galv]

glog-like functions are annoying to implement. We did that for kaldi, as people here are aware. Implementing KALDI_ERROR macro is actually pretty complicated because it requires throwing an exception in a destructor.

Also, glog, uses poor-ly named space macros like LOG, ERROR, etc.,so you may as well just use glog, in case another library also depends on it.

So I think glog is fine.

[csukuangfj]

@galv @qindazhu
thanks, I'll include glog in later commits.