Create /branches/issue-840-dev as a copy of 2901:/trunk.

This is the branch I'm going to work on to rearrange our network
protocol (property namespaces.)  Both libsvn_ra_dav and mod_dav_svn
will be changed.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/issue-840-dev@842976 13f79535-47bb-0310-9956-ffa450edef68