The core and compat codebase have code to support SVN pre 1.7. I have tested it with 1.6, and it looks *roughly* correct, but our code does not work, and has not worked since Feb 2014 as detailed at
https://phabricator.wikimedia.org/T95077
In addition, SVN 1.6 is no longer supported by the SVN developers.
As a result, I doubt that anyone is relying on support for SVN 1.6 or earlier, and I would like to remove support for SVN pre 1.7.
Please yell out if there is a reason to keep supporting SVN 1.6 ...?