services: also clear DataFlowInterface in Service::clear()

Signed-off-by: Johannes Meyer <johannes@intermodalics.eu>
Merge branch 'toolchain-2.7'
Merge branch 'unbuffered-connpolicy' of https://github.com/meyerj/rtt into toolchain-2.7
Merge branch 'service-clear-dataflowinterface' of https://github.com/meyerj/rtt into toolchain-2.7
Merge branch 'global-service-cleanup' of https://github.com/meyerj/rtt into toolchain-2.7
Merge branch 'per-package-env-hook' into HEAD
fixing devel pc creation
reverting 112f7f8df41c9fa1f0ce8a590f1f5899512db78f
Making it so orocos_use_package doesn't add excessive flags from packages that were found through some other means
Update .travis.yml