The only thing in helpers.py that needed vars.py was the log stuff.

So put it in its own file.  Now it's safer to import and use helpers even if
you can't safely touch vars.

redo-ifchange.py

@@ -1,7 +1,8 @@
 #!/usr/bin/python
 import sys, os, errno, stat
 import vars, state, builder, jwack
-from helpers import debug, debug2, err, unlink
+from helpers import unlink
+from log import debug, debug2, err
 
 def _nice(t):
     return state.relpath(os.path.join(vars.BASE, t), vars.STARTDIR)