This includes a fairly detailed test of various known shell bugs from the
autoconf docs.
The idea here is that if redo works on your system, you should be able to
rely on a *good* shell to run your .do files; you shouldn't have to work
around zillions of bugs like autoconf does.
We were hardcoding the absolute $LIBDIR location, which sounds smart, but not if
you're doing "make install" into a temp dir that will end up somewhere else
later.
Instead, look for ../lib/redo/ from wherever the binary is installed.
