Add a hacky environment variable that lets me arrange a soak-test of a

Add a hacky environment variable that lets me arrange a soak-test of a
solver I've just modified, by forcing every game generation to be
instantly followed by an attempt to re-solve the same game
_description_ without the aux_info.

I've hacked similar changes in to midend.c several times in the last
couple of months for one reason or another, and it's about time I
arranged not to have to recompile to do it!

[originally from svn r9549]