Also known as "forward history searching", this enhancement brings to the
libsvn_fs API the ability to traverse the chain of "interesting history points"
for a line of versioned history in an oldest-to-youngest fashion. Today's API
allows only the opposite: starting with a path/revision pair, walk backwards
through the past changes in that line of history. This functionality flows
naturally out of the current FS design, which stores for each node-revision a
reference to that node-revision's predecessor node-revision. Currently there is
no FS-level storage of the reverse-link -- the successor node-revisions. And
yes, there's a 1-to-many relationship of node-revisions to their successors
because successors are created both by modifications to a versioned item and by
copying those items elsewhere (which can happen any number of times).