loader: Change version calculation to be more consistent.

Use 1000 * major + minor when calculating the version number that
gets set in the Ficl environment or lua loader property. This allows
for more room if the minor number needs to go above 9.

Add loader.version property to lua loader.

Reviewed by: imp
Obtained from: Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D39631