Move atoi() into atoi.py and add a new debug2() debug level.

atoi() was getting redundant, and unfortunately we can't easily load
helpers.py in some places where we'd want to, because it depends on vars.py.
So move it to its own module.

jwack.py

@@ -2,6 +2,7 @@
 # beware the jobberwack
 #
 import sys, os, errno, select, fcntl
+import atoi
 
 _toplevel = 0
 _mytokens = 1
@@ -14,13 +15,6 @@ def _debug(s):
         sys.stderr.write('jwack#%d: %s' % (os.getpid(),s))
     
 
-def _atoi(v):
-    try:
-        return int(v or 0)
-    except ValueError:
-        return 0
-
-
 def _release(n):
     global _mytokens
     _debug('release(%d)\n' % n)
@@ -60,8 +54,8 @@ def setup(maxjobs):
         s = flags[ofs+len(FIND):]
         (arg,junk) = s.split(' ', 1)
         (a,b) = arg.split(',', 1)
-        a = _atoi(a)
-        b = _atoi(b)
+        a = atoi.atoi(a)
+        b = atoi.atoi(b)
         if a <= 0 or b <= 0:
             raise ValueError('invalid --jobserver-fds: %r' % arg)
         try: