rewriteutil: fix crash when a rewritten message references f{6,64} Without this, the rewriteutil logic thinks it's found a reference to the wdir pseudo-revision, and then tries to look it up and rewrite it. Stop it from doing that. Amusingly, I had trouble working with this changeset when I didn't describe the defect above using a regular expression, because it would trigger the bug in my installed version of hg. Differential Revision: https://phab.mercurial-scm.org/D11232