Add the autorevision tool to Wesnoth.

This version used is 1.4 and is copied from [1].

[1] http://www.catb.org/esr/autorevision/
Adds autorevision based revision numbers.

Partial cherry-pick of 43f617179ec1ec6e770cdabee28959d534bf35f5
for game_config.cpp only
Made the version string from autorevision...

...also include base version from wesconfig.h
Added support for autorevision to scons