WebDAV performance issues with Global Spaces resource

A Confluence instance that has a large number (100's) of spaces will exhibit performance issues with the Confluence WebDAV plugin. Response times will average around 5-10 seconds to get the list on a warmed cache. In some extreme cases, response times of up to 180 seconds have been observed from a cold-cache request.

The problem is actually fairly simple - GlobalSpaceResourceImpl is issuing a query to get a list of all spaces that the currently authenticated user can access. Once this list has been built, the AbstractCollectionResource.getMembers() method will then iterate over each collected SpaceResourceImpl, and do individual permission checks on each one. These checks are inefficient and (should be) entirely unnecessary.