OSX NFD normalization confuses repo move check

[jast]

In cache.py:

if previous_location and previous_location != repository_location:
    msg = ("Warning: The repository at location {} was previously located at {}\n".format(
# [snip]

This works fine but NFD can make for confusing warnings if the repo path contains special characters and you access the repo via . (or $(pwd)) sometimes. To reproduce:

cd /tmp
mkdir empty
borg init -e none tëst
borg create tëst::test1 /tmp/empty
cd tëst
borg create .::test2 /tmp/empty
>> Warning: The repository at location /private/tmp/tëst was previously located at /private/tmp/tëst
>> Do you want to continue? [yN] 

[enkore]

Some background: mpv-player/mpv/issues/1492