svnwrap: add subvertpy wrapper Subvertpy is, in many ways, a better interface to Subversion than the SWIG bindings. It's faster, leaks less and offers a cleaner API. The added wrapper is able to coexist with the SWIG wrapper, and not enabled by default. In order to allow this, the wrapper adapts the output from Subvertpy so that it is similar to the output from the SWIG bindings. An example of this can be seen in the modules that work with editors: the nested editors offered by Subvertpy had to be flattened to work with our editor code. This change does not activate the Subvertpy wrapper, yet, and thus does not affect any functionality.