This updates the Subversion unit tests to build a SCNClient in each

test where it's needed, rather than in setUp(). This is in prepration

for new tests that will need to handle client construction differently.
This also cleans up a lot of the assertions to be less verbose and to be

more comprehensive.
We had a lot of combinations of checking instance type, key presence,

and then values, but this is far less useful (less accurate) than just

checking dictionaries for equality. We missed things because we weren't

doing these checks.
It also fixes up diff checking to compare for content and not just a

hash, for each version of Subversion where we previously compared

hashes. This will be important for work on supporting alternative diff

tools.

Subversion unit tests pass.