fsfsfixer script not compatible with 1.8+ repos

Hi all,

I'm attempting to fix a corrupt repository which is reporting "Checksum
mismatch while reading representation" (the possible cause has been raised
by Julian - https://svn.haxx.se/dev/archive-2017-01/0080.shtml).

I'm wanting to run the fsfsfixer script from
https://svn.apache.org/repos/asf/subversion/trunk/contrib/server-side/fsfsfixer/
but this isn't compatible with repositories created in 1.8+, as per the
error I'm seeing:

('error:', FixError("Filesystem '/path/to/repo/db' is too new (format 6);
try the version at
https://svn.apache.org/repos/asf/subversion/trunk/contrib/server-side/fsfsfixer
",))

I see there is the setting "MAX_FSFS_FORMAT = 5" in the file
fixer/fix-rev.py whiuch I could in theory change to 6, but I don't know if
the format is too different to get away with this.

For good measure, here is some information about the repo:

UUID: bf4578a2-f9f2-0310-8dae-8c7b66b38d95
Repository Format: 5
Compatible With Version: 1.8.0
Repository Capability: mergeinfo
Filesystem Type: fsfs
Filesystem Format: 6
FSFS Sharded: no
FSFS Logical Addressing: no

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