Set travis to test old versions of numpy and scipy too
Remove redundant yet unstable test_spectral_lobpcg_mode

The lobpcg mode is already tested in the test_spectral_clustering test.

LinAlgError was raised when executing test_spectral_lobpcg_mode on some
systems depending on the version of the scipy and LAPACK libraries.
More robust and informative bayes regression test
Skip known failure in scipy 0.11.0
TST: more robust test of dropping in Lars