Added src-libs subdirectory for keeping source code to extra libs. These
are things that are needed, but that many systems already have packages
available to install, and many users may have versions of these already
installed to support other projects. So rather than build and install by
default with the main SimGear build/install, these are kept separate so that
those users that don't have them already installed can build and install
them separately.
projects / simgear.git / commit