URLs provided as parameters to subvertpy.client.Client methods must
be quoted or an assertion will be raised by libsvn otherwise.
Issue found while attempting to fix the loading of svn://tug.org/texlive
```name=test_export.py,lang=python
from urllib.parse import quote
import sys
from subvertpy import client
from subvertpy.ra import (
Auth,
RemoteAccess,
get_simple_prompt_provider,
get_username_provider,
)
auth_providers = [get_username_provider()]
client = client.Client(auth=Auth(auth_providers))
url = "svn://tug.org/texlive/trunk/Build/source/libs/teckit/docs/Calling TECkit from VB.doc"
if len(sys.argv) > 1 and sys.argv[1] == "quote":
url = quote(url, safe=":/")
client.export(url, to="/tmp/export_test", rev=3455, peg_rev=3455, overwrite=True)
```
```
$ python test_export.py
python: ../subversion/libsvn_subr/dirent_uri.c:1562: uri_skip_ancestor: Assertion `svn_uri_is_canonical(child_uri, NULL)' failed.
Aborted
$ python test_export.py quote
$ echo $?
0
```