errors: move similarity_hint() to error module...
errors: move similarity_hint() to error module
I want to be able to reuse it from `UnknownIdentifier`'s constructor.
Moving it results in a new import of `difflib` in the `error`
module. There was a comment at the top of `error.py` saying "Do not
import anything but pycompat here, please", which was added (except
for the "pycompat" bit) in
08cabecfa8a8 (errors: move revlog errors,
2009-01-11). I don't know the reason for the comment. I'm guessing the
point was to not make the module depend on other Mercurial modules. If
that was it, then importing `difflib` should be fine.
Sorry about the churn (I moved this code from the `dispatch` module to
the `scmutil` module very recently).
Differential Revision:
https://phab.mercurial-scm.org/D9345
