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.

jwack.py

@@ -2,7 +2,7 @@
 # beware the jobberwack
 #
 import sys, os, errno, select, fcntl, signal
-import atoi
+from helpers import atoi, close_on_exec
 
 _toplevel = 0
 _mytokens = 1
@@ -83,8 +83,8 @@ def setup(maxjobs):
         s = flags[ofs+len(FIND):]
         (arg,junk) = s.split(' ', 1)
         (a,b) = arg.split(',', 1)
-        a = atoi.atoi(a)
-        b = atoi.atoi(b)
+        a = atoi(a)
+        b = atoi(b)
         if a <= 0 or b <= 0:
             raise ValueError('invalid --jobserver-fds: %r' % arg)
         try:
@@ -242,7 +242,6 @@ def start_job(reason, jobfunc, donefunc):
         finally:
             _debug('exit: %d\n' % rv)
             os._exit(rv)
-    from helpers import close_on_exec
     close_on_exec(r, True)
     os.close(w)
     pd = Job(reason, pid, donefunc)