Transmission is a lightweight open source BitTorrent client, providing
useful functionality without feature bloat. It consists of a daemon, a
GTK+, Qt and CLI client.

By default, all 4 components are built. Specific parts can be disabled
by setting one or more environment variables:

GTK=no
QT=no
CLI=no
DAEMON=no

At least one component must be enabled (so all 4 set to "no" won't work).
