builder.py: we weren't stamping .do files correctly if dodir!='.'.

The result was that t/deps/dirtest was actually failing in some cases.  But
it wasn't failing quite reliably enough, because the failing test was
dirtest/dir1/all, which has the same name as some other 'all' files,
confusing the issue.  Renamed dirtest/dir1/all.do to dirtest/dir1/go.do instead.

Reported by Prakhar Goel and Berke Durak.

builder.py

@@ -154,7 +154,7 @@ class BuildJob:
         self.argv = argv
         sf.is_generated = True
         sf.save()
-        dof = state.File(name=dofile)
+        dof = state.File(name=os.path.join(dodir, dofile))
         dof.set_static()
         dof.save()
         state.commit()

t/deps/dirtest/t1.do

@@ -1,2 +1,2 @@
-redo-ifchange dir1/all
+redo-ifchange dir1/go
 echo $$ >>log