If a and b both depend on c, and c is a static (non-generated) file that has
changed since the last successful build of a and b, we would try to redo
a, but would forget to redo b. Now it does both.
If a file previously was generated but now isn't (ie. its .do file
disappears), we would never re-stamp that target, and so all its
dependencies would rebuild continually.
.do files should never modify $1, and should write to *either* $3 or stdout,
but not both. If they write to both, it's probably because they forgot to
redirect stdout to stderr, a very easy mistake to make but a hard one to
detect.
Now redo detects it for you and prints an informative message.
Now 'redo test' runs the tests, but 'redo t' just builds the programs.
Also removed wvtest stuff; we're not really using it properly anyway and
it's not helping our testing right now. It might come back later.
