add-some-regression-tests-for-sequence (patch 1 of 1)

'git apply --summary --stat --apply --verbose' output was:

 src/test/regress/expected/sequence.out |  320 ++++++++++++++++++++++++++++++++
 src/test/regress/sql/sequence.sql      |  200 ++++++++++++++++++++
 2 files changed, 520 insertions(+), 0 deletions(-)

For original context, see http://www.postgresql.org/message-id/CAEP4nAyZXv-nSWDxKpdKtDFXX+35G+6=dZFYxH7k0LKyH0dgdA@mail.gmail.com
Adding travis.yml