On the 'move-tracking-2' branch: Refactoring towards moving the subbranch-root element concept to a higher level. Represent a subbranch-root payload by a payload object with a flag set, rather than by null, and eliminate some special handling of a subbranch-root element.
* subversion/include/private/svn_branch.h, subversion/libsvn_delta/branch.c (svn_branch_instantiate_elements): Rename from 'svn_branch_instantiate_subtree'. Don't take new parent-eid and name parameters; instead, take these from the 'elements' input.
* subversion/libsvn_delta/compat3e.c (editor3_branch): Adjust the caller.
* subversion/svnmover/svnmover.c (do_branch_into): Adjust the caller.