Rename vars{,_init}.py -> env{,_init}.py.

This fixes some pylint 'redefined builtins' warnings.  While I was
here, I fixed the others too by renaming a few local variables.

redo/paths.py

@@ -1,5 +1,5 @@
 import os
-import vars
+import env
 from logs import debug2
 
 
@@ -15,7 +15,7 @@ def _default_do_files(filename):
 
 def possible_do_files(t):
     dirname, filename = os.path.split(t)
-    yield (os.path.join(vars.BASE, dirname), "%s.do" % filename,
+    yield (os.path.join(env.BASE, dirname), "%s.do" % filename,
            '', filename, '')
 
     # It's important to try every possibility in a directory before resorting
@@ -24,7 +24,7 @@ def possible_do_files(t):
     # the former one might just be an artifact of someone embedding my project
     # into theirs as a subdir.  When they do, my rules should still be used
     # for building my project in *all* cases.
-    t = os.path.normpath(os.path.join(vars.BASE, t))
+    t = os.path.normpath(os.path.join(env.BASE, t))
     dirname, filename = os.path.split(t)
     dirbits = dirname.split('/')
     # since t is an absolute path, dirbits[0] is always '', so we don't