New Micro AI: Fast AI

This AI is meant as a fall-back AI for scenarios where there are so
many units that attacks and moves done by the default AI are slow with
long delays before each move. It replaces the default combat and
move-to-targets candidate actions.
See http://wiki.wesnoth.org/Micro_AIs
Fast Micro AI: use wesnoth.require instead of wesnoth.dofile
Fast Micro AI: exclude guardians from move-to-targets CA
Fix bug #21372: fix unit move continuation if enemy discovered
add wesnoth-test text domain to a unit test which was missing it
fixup test utils to accomodate recent test directory change

Previously, the C++ unit tests which used the test utils
game config manager object would load things in /data/test/,
and not all of /data/. Presumably this was for efficiency
of the C++ unit tests.

I didn't realize this when working on the wml unit tests branch.
In that branch, I added all of the WML unit test macros and
scenarios to data/test/, and found that I couldn't load them,
since /data/_main.cfg had the {/test/_main.cfg} line commented
out. I uncommented this and made some other changes in
/data/test/ so that loading wml unit tests would work.

However, it made the C++ unit tests not happy.
This change makes them not create errors, but it also includes
all of core when they run, which may not have been intended,
although I don't see that it causes problems.

I may fix this all up soon, by making a different environment
for C++ and WML unit tests. (In fact this already existed,
and I have now destroyed the distinction.) Putting WML
tests in their own directory different from the C++ tests
may be the simplest fix, that will preserve the environment
of the old C++ tests while giving a more complete environment
where the WML unit tests may run.
Merge branch 'master' of https://github.com/wesnoth/wesnoth