Coveralls defaulted to using gcov for all builds even when using clang
in which case it should have used llvm-cov. Fix this by specifying
different coveralls commands for each compiler.
Additionally, move the coverage to commands to the after_success section
to avoid sending coverage data when the build failed.
Indentation in travis.yml was inconsistent, update it to consistently
use 2 spaces.
I considered using 4 spaces to be more consistent with the rest of the
project but it looks too spaced out and doesn't suit YAML in my opinion.
Since we only use sudo for installing packages, start using the apt
travis addon for the installation in order to allow container-based
builds to be used for testing dunst which should theoretically have a
faster boot time.
Change the behaviour of travis to only notify if the build status
changes. The previous behaviour which was notifying for every build
regardless of status added a lot of unnecessary noise to the IRC
channel.
Remove xext and xft as a dependency since they are not currently used
and probably haven't been used a while.
Also remove freetype2 from the pkg-config list, while it is required by
pangocairo it should be included from the pkg-config --cflags call.
