Ignore "_ignore.txt" files when counting errors we want to fix sometime.

BUG=5469
TEST=make sure errors in _ignore files in, say, base/data/purify/ don't show
  up in the buildbot's count of errors we need to fix
Review URL: http://codereview.chromium.org/17457

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@7844 0039d316-1c4b-4281-b951-d872f2087c98

tools/purify/purify_analyze.py

@@ -629,6 +629,7 @@ class PurifyAnalyze:
       if (not os.path.basename(path).startswith(self._name) or
           not path.endswith(".txt") or
           path.endswith("gtest.txt") or
+          path.endswith("_ignore.txt") or
           not os.path.isfile(path)):
         continue
       msgs = self._MessageHashesFromFile(path)