workaround for "make: don't know how to make w. Stop"

This problem happens if the outer make is GNU make, and there's at
least one recursive make invocation. In this case GNU make sets the
MAKEFLAGS environment variable to "w". But some test scripts may call
freebsd-make or pmake, and the content of the MAKEFLAGS variable is
interpreted as the (non-existing) target w.

Fix is to unset the MAKEFLAGS variable before calling freebsd-make,
pmake, or BSD's native make.
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
added DB_File as a prereq

Usually installed with Perl itself, but may be missing, e.g.
with self-compiled Perls (perlbrew! travis!).
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