Make release scripts even more robust.

tools/release/releases.py

 #!/usr/bin/env python
 # Copyright 2014 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script retrieves the history of all V8 branches and
 # their corresponding Chromium revisions.
 
 # Requires a chromium checkout with branch heads:
 # gclient sync --with_branch_heads
@@ skipping 316 matching lines @@
       self.Die("DEPS file not present.")
 
 
 class UpdateChromiumCheckout(Step):
   MESSAGE = "Update the checkout and create a new branch."
 
   def RunStep(self):
     cwd = self._options.chromium
     self.GitCheckout("master", cwd=cwd)
     self.GitPull(cwd=cwd)
+    self.DeleteBranch(self.Config("BRANCHNAME"), cwd=cwd)
     self.GitCreateBranch(self.Config("BRANCHNAME"), cwd=cwd)
 
 
 def ConvertToCommitNumber(step, revision):
   # Simple check for git hashes.
   if revision.isdigit() and len(revision) < 8:
     return revision
   return step.GetCommitPositionNumber(
       revision, cwd=os.path.join(step._options.chromium, "v8"))
 
@@ skipping 134 matching lines @@
                               "candidates."))
     parser.add_argument("-c", "--chromium",
                         help=("The path to your Chromium src/ "
                               "directory to automate the V8 roll."))
     parser.add_argument("--csv", help="Path to a CSV file for export.")
     parser.add_argument("-m", "--max-releases", type=int, default=0,
                         help="The maximum number of releases to track.")
     parser.add_argument("--json", help="Path to a JSON file for export.")
 
   def _ProcessOptions(self, options):  # pragma: no cover
+    options.force_readline_defaults = True
     return True
 
   def _Config(self):
     return {
       "BRANCHNAME": "retrieve-v8-releases",
       "PERSISTFILE_BASENAME": "/tmp/v8-releases-tempfile",
     }
 
   def _Steps(self):
     return [
       Preparation,
       RetrieveV8Releases,
       SwitchChromium,
       UpdateChromiumCheckout,
       RetrieveChromiumV8Releases,
       RietrieveChromiumBranches,
       CleanUp,
       WriteOutput,
     ]
 
 
 if __name__ == "__main__":  # pragma: no cover
   sys.exit(Releases().Run())