Search parent directories for default*.do.

Previously, we would only search for default*.do in the same directory in
the target; now we search parent directories as well.

Let's say we're in a/b/ and trying to build foo.o.  If we find
../../default.o.do, then we'll run

	cd ../..; sh default.o.do a/b/foo .o $TMPNAME

In other words, we still always chdir to the same directory as the .do file.
But now $1 might have a path in it, not just a basename.

t/.gitignore

@@ -1,9 +1,3 @@
-c
-c.c
-c.c.c
-c.c.c.b
-c.c.c.b.b
-d
 test.args
 test2.args
 /passfail