configure: Add support for GeoIP without pkg-config

If libgeoip is installed without a pkg-config data file, then fall
back to GEOIP_LIBS and GEOIP_CFLAGS, if set.

On systems that do not have the pkg-config data file for libgeoip,
running configure with GEOIP_LIBS and GEOIP_CFLAGS appropriately set,
along with --with-geoip, will enable the module.

Reported-by: Peter Czanik <czanik@balabit.hu>
Signed-off-by: Gergely Nagy <algernon@balabit.hu>
travis: Simplify the config

We only need one apt-get install line, and no template for the IRC
notifications, the default is good enough.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>