Always print GIT_VERSION even if empty

Adjustment from last proposed patch. Less crowded and more standard.
This should not break any packaging.

feedback?

Signed-off-by: Jonathan Rajotte Julien <jonathan.r.julien@gmail.com>
Add --disable-git-version to configure

By default, GIT_SOURCE variable is defined to 1. The disable option
makes the configure to NOT define it.

This way, anyone not wanting the git version like for instance packager
building from the git repository, it can be used to remove it.

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: always use git describe --all --long for the git version

Signed-off-by: David Goulet <dgoulet@efficios.com>