convert: convert URLs to UTF-8 for Subversion
Preamble: for comprehension, note that the `path` of geturl() would better be
called `path_or_url` (the argument of the call of getsvn() is called `url`).
For HTTP(S) URLs, the changes don’t make a difference, as they are restricted to
ASCII.
For file URLs, the reasoning is the same as for paths: we have to roundtrip with
what Subversion is doing.
When the locale encoding is ISO-8859-15, trying to convert a SVN repo
`file:///tmp/a€` failed before like this:
file:///tmp/a%A4 does not look like a Subversion repository to libsvn version 1.14.0
Decoding the path using the locale encoding can fail. In this case, we have to
bail out, as Subversion won’t be able to do anything useful with the path.
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https://www.mercurial-scm.org/wiki/ContributingChanges
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commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).