Sometimes we want to restrict the acceptable versions to a list of
versions, or a smallest-version + largest-version, or both. For
instance, GStreamer's opencv plugin is only compatible with
3.1.0 >= opencv >= 2.3.0
In the case the main project set a subproject for a dependency another
subprojects uses, that other subproject should rather use the first
subproject rather that using native dependency.
For example in gst-all we set all GStreamer modules as subprojects
and, gst-plugins-base is set after gstreamer core, and
we want gst-plugins-base to always use GStreamer core from the subproject
and not the possibly avalaible native one.
And remove the InternalDependencyHolder class.
In some cases we need to know the type of dependency we are
dealing with. For example in GStreamer if the dependency
is not an internal one, then we need to get some env var
from pkg-config to know where to find some plugins necessary
to run some tests.
Nirbheek Chauhan
Thibault Saunier