On the 'move-tracking-2' branch: Add a comment about element ids being arbitrary.
On the 'move-tracking-2' branch: Add a comment about element ids being
arbitrary.

* subversion/include/private/svn_branch.h,
  (svn_branch_eid_t): Add a comment.

git-svn-id: 486ec3464084f62cfe8608152673c827b947faa2@1676582 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion