[ENH] improve the way rdiff-backup handles long filenames under Windows

[ericzolf]

Is your feature request related to a problem? Please describe.

Increase the filename length in the tests testing/location_map_filenames_test.py resp. testing/action_backuprestore_test.py so that files can still be created, but fail to be backed-up and then fix the issue, as files should get the shorter name mapped to accommodate for Windows quirks not properly reporting a filename length issue.

Also revisit the testing/longnametest.py test.

Describe the solution you'd like

I don't know yet.

Describe alternatives you've considered

Just ignore Windows quirks...

Additional context

Windows complains about file not existing:

WARNING: UpdateError:
         'C:/Users/vagrant/Develop/rdiff-backup/dist/rdb/testfiles/location_map_filenames/bak/rdiff-backup.tmp.1'
         [Errno 2] No such file or directory:
         b'C:/Users/vagrant/Develop/rdiff-backup/dist/rdb/testfiles/location_map_filenames/bak/rdiff-backup-data/increments/long;070i;076n;065mlong;070i;076n;065mlong;070i;076n;065mlong;070i;076n;065mlong;070i;076n;065mlong;070i;076n;065mlong;070i;076n;065mlong;070i;076n;065m.1970-01-01;08405-33-21;090.diff.gz'