OTWO-3206: Fix utf-8 encoding issues for svn and git

This fixes encoding issues in svn repositories. It also fixes encoding issues in git when `verbose_commit` method is used.

It is not possible to emulate an invaliding encoding scenario with svn 1.6.6 or 1.8.8. Since older versions of svn are not available from apache or ubuntu, we cannot replicate the scenario. In order for the tests to fail, we mock the svn utility so that `svn log` returns content with invalid encoding.