TST: silence deprecationwarning from signal module in test output.
TST: mark io.savemat test with OrderedDict as knownfail if it fails. See #1874
ENH: faster and more memory-efficient version of connected-components algorithm

Replaces the recursive algorithm with an iterative algorithm and adds extra
tests for weakly and strongly connected components.

Backport of PR-460.

Address review comments: Use ITYPE instead of np.int32. Shorten long lines
GEN: regenerate csgraph/_traversal.c from Cython source.
TST: add regression test for connected components, see ticket 1876.

Backport of PR-484.