Ubuntu 14.04 ships with apt 0.9.15, has a ``fancy progress bar'', which
is a green bar that shows at the bottom of the terminal showing progress
throughout install.
This patch enables the progress bar, which is usually done by running
echo 'Dpkg::Progress-Fancy "1";' > /etc/apt/apt.conf.d/99progressbar
This commit changes the proxy file name to be more consistent with other files
in `apt.conf.d`. The old file (`apt.conf.d/proxy`) is removed.
Tests has been updated.
We already had a feature to manage and purge entries in preferences.d
but not the preferences file in /etc/apt. This commit adds that
capability.
Fixes#199
