new_comments.pl: use Tie::IxHash only for 5.18

Also, if used, then a new Tie::IxHash (>= 1.23) is required, because
of a "delete while iterating" bug, see
https://rt.cpan.org/Ticket/Display.html?id=82248
first steps for travis testing

* don't prereq "difficult" modules like Image::Magick or X11::Protocol
* use "test-no-cgi" target
added .travis.yml
added Geo::Proj4 to list of uninstallable dependencies
travis build: removed 5.8 because of DBD::XBase issues
travis: added GD and dependencies to the list of uninstallable dependencies
travis: install deps via apt-get, call "make ext"
more system prereqs needed for Geo::Proj4 and DB_File under Ubuntu
.travis.yml: added agrep to list of pre-installed packages
.travis.yml: added reasons for installing packages
.travis.yml: installing GD should work now
travis testing: define BBBIKE_TEST_FOR_LIVE=1

So bbbikedraw.t won't try to test the ImageMagick backend.
.travis.yml: installing missing fonts