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.

builder.py

@@ -1,6 +1,7 @@
 import sys, os, errno, stat
 import vars, jwack, state
-from helpers import log, log_, debug, debug2, err, warn, unlink, close_on_exec
+from helpers import unlink, close_on_exec
+from log import log, log_, debug, debug2, err, warn
 
 
 def _possible_do_files(t):