trunk: fix bug in nnet-component.cc introduced in revision 4581 (2 days ago), which strongly affected speed of nnet2 training.

git-svn-id: https://svn.code.sf.net/p/kaldi/code/trunk@4590 5e6a8d80-dfce-4ca6-a32a-6e07a63d50c8
trunk: multiple fixes to recently modified splicing code (apologies, nnet2 training code may not have been working correctly in the last couple of days).

git-svn-id: https://svn.code.sf.net/p/kaldi/code/trunk@4592 5e6a8d80-dfce-4ca6-a32a-6e07a63d50c8
trunk: for splicing component: adding tests, bug-fix in backprop of splice component (should not affect current scripts)

git-svn-id: https://svn.code.sf.net/p/kaldi/code/trunk@4594 5e6a8d80-dfce-4ca6-a32a-6e07a63d50c8