Can't upgrade to Bamboo 2.0 or save plan configuration, due to Bamboo trying to write invalid SVN external definition to XML

Bamboo tries to save the external definition data along with the plan. And if the SVN external definition follows a nested path with several directories, e.g: third-party/b. Bamboo tries to save this path with the / and this throws an invalid XML character error.

This prevents users from editing a plan with SVN:Externals defined in Bamboo 2.0/beta or updating to Bamboo 2.0 from Bamboo 1.2.4