This reverts commit 6e893e8a.

Switch to plain composer.

Kristoffer Wiklund authored Jul 25, 2014 and Herman van Rink committed Jul 25, 2014

Issue #2275467 by kristofferwiklund: Fixed incorrect variable in Debian postinstall script for Apache 2.4

this greatly improves overall performance during mass migrations, at the
cost of slower job processing

requested and sponsored by praxis

Conflicts:
	debian/aegir2-provision.postinst

the rationale for upgrades is obvious: even if the next package will
restore the link, the upgrade may fail and then all sites go
down. even if it doesn't fail, sites go down for the duration of the
upgrade: bad. this affects 1.x to 2.x upgrades.

the rationale for remove is that we don't completely destroy the data,
so the sites are expected to remain.

we also cleanup after ourselves in special corner cases
(abort-install, disappear) as well.

this is to allow more flexibility during upgrades (and even installs,
actually). for example it allows the admin to change the location of
the aegir home to be (say) /srv/aegir instead of /var/aegir

see https://drupal.org/node/2118857

see https://drupal.org/node/2002114