This adds typing throughout the Subversion codebase, ensuring

consistency in calls, results, and dictionary contents.
There are some fixes for some bad assumptions in the code, and some

minor changes to the base SCMTool class to make

parse_diff_revision()'s parameters consistent with the built-in

SCMTools.
Changes will build upon this to improve operation invocation and error

handling, in preparation for the new SSL management.

Unit tests pass.