In order for our g_info()/g_message()/g_debug() log messages to be
handled, we need to have G_MESSAGES_DEBUG=Tracker enabled in the
environment. Previously we would enable G_MESSAGES_DEBUG=all, which
has the effect of also enabling log output from GLib/GIO and other
dependencies.

In the interests of keeping logs clean, we now require the user to
explicitly set G_MESSAGES_DEBUG=all if they want maximum debug output.