Rename "dir" variables

The variable name "dir" conflicts with the name of a Python built-in
function: http://docs.python.org/library/functions.html#dir

Change-Id: I850f3ec8df7563dc85e21f2876fe5e6550ca2d8f

main.py

@@ -209,8 +209,8 @@ def _CheckWrapperVersion(ver, repo_path):
     cp %s %s
 """ % (exp_str, _MyWrapperPath(), repo_path)
 
-def _CheckRepoDir(dir):
-  if not dir:
+def _CheckRepoDir(repo_dir):
+  if not repo_dir:
     print >>sys.stderr, 'no --repo-dir argument'
     sys.exit(1)