Improve travis-ci integration

As now we probe for some kernel features, it is important that we try to build the library against different kernel headers.
That's what the first patch does.

patch 2 and 3 seize the moment to build using different compilers/versions and patch 4 minimize emails by only sending build fail/success if it changes.

Build status can be seen at https://www.travis-ci.org/sctp/lksctp-tools

Marcelo Ricardo Leitner (4):
travis: build against multiple kernel versions
travis: build against multiple gcc versions
travis: build against multiple clang versions
travis: only send notifications if build status changed

 .travis.yml            | 110 ++++++++++++++++++++++++++++++++++++++---
 .travis/linux-build.sh |  43 ++++++++++++++++
 2 files changed, 147 insertions(+), 6 deletions(-)
 create mode 100755 .travis/linux-build.sh

2.17.1

Applied.