Dict::c_handler() is const, avoid const_cast

Whyever gcc 4.6.3 on Ubuntu 12.04 LTS (travis build farm) complained about our
const_cast syntax:
 src/bindings/cpp/shortcuts.cpp:33:42: error: expected < before <: token
... we can simply avoid that evil const_cast at all.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
travis-ci: import travis yaml controller

.travis.yml is used for automatic builds on travis build farm
(https://travis-ci.org/) if the travis service hook is enabled for the
repo on github.

This inital yaml controller will run 2 different compilers (gcc, clang). The
test suite currently fails, that's why we don't abort yet.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>