tags: show how hg behaves if a tags cache entry is truncated
I'm seeing an error of this form in production on the order of once a
month. I'm not sure how it happens, but I suspect interrupting a pull
might result in half written cache entries.
Differential Revision: https://phab.mercurial-scm.org/D8094
#require docutils gettext
$ $TESTDIR/check-gendoc zh_TW
checking for parse errors