Introduce EXTRA_VERSION_NAME and EXTRA_VERSION_DESCRIPTION

On version.i generation, check the content of the following files :

  * "extra_version_name"

    The first line is used to populate the EXTRA_VERSION_NAME pre-processor
    define statement.

  * "extra_version_description"

    The content is used to populate the EXTRA_VERSION_DESCRIPTION pre-processor
    define statement.

    It should contain the description of local modifications done to the tree.
    This can be used by distribution packager to specify what changes were
    applied locally. Mostly in the form of patch/commit name. All non-alpha
    numeric characters are converted to "-".

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>