tests/test-bad-extension.out

verify: fix "missing revlog!" errors for revlog format v0 and add test

With revlog format v0 the .d files are empty if the only revision stored is an
empty file. Since Mercurial can no longer create format v0 repositories, but
still use it, add a script which creates a repository with a single empty file.
This can be used in other tests if wanted.

*** failed to import extension badext from .../badext.py: bit bucket overflow
*** failed to import extension badext2: No module named badext2
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