t/all.do: use redo instead of redo-ifchange.

I'm not quite sure what I was thinking, using redo-ifchange there, but
the result was that some tests wouldn't run if you run 'redo test'
repeatedly, even after modifying redo itself.

Also tweaked t/950-curse so that it always runs, not just the first
time.

t/950-curse/all.do

@@ -1,3 +1,5 @@
+rm -f *.n[012]
+
 . ./check-1.sh
 redo-ifchange 1.n0 2.n0 3.n0
 DEPS=$(./seq 10 | sed 's/$/.n1/')