ChangeLog: add changes to internal data structures

Covers commits:

1c83a65 btrbk: add filter capabilities to vinfo_subvol_list
a25487e btrbk: cosmetics (log messages)
ef5c369 btrbk: use _is_same_fs_tree() where applicable
0454f60 btrbk: bugfix: match btrbk_basename in get_latest_snapshot_child()
2c1c3b4 btrbk: cleanup: remove snapshot_dir, rename sroot->snaproot
c457540 btrbk: use separate vinfo for snapshot directory (allows snapshot_dir to be a mountpoint)
f5dc4e0 btrbk: add known mountpoints to btr_tree nodes as anchor for reverse lookup
e9374b3 btrbk: replace url_cache by spec_cache
0ea0430 btrbk: cleanup (cosmetics, documentation)
b37ef84 btrbk: always read mountpoints; include all snapshots from mountpoint as candidates for best common parent
b549e11 btrbk: raw targets: move tree readin to separate function; add caching
7a1bc25 btrbk: raw targets: create fake btr_tree instead of maintaining separate list
6c502cb btrbk: search complete target tree for correlated subvolumes

ChangeLog

@@ -1,10 +1,20 @@
 btrbk-0.27.0-dev
 
+  * MIGRATION
+    - update ssh_filter_btrbk.sh on remote hosts (btrbk always calls
+      "readlink" and "cat /proc/self/mounts").
   * Add "preserve_hour_of_day" configuration option (close #202).
   * Bugfix: correct scheduling of "first weekly backup in month/year"
     (close #217). Note that this change may result in (previously
     preserved) backups to be deleted!
   * Bugfix: add "btrfs filesystem usage" backend mapping (close #222).
+  * Enhance internal data structures:
+    - Allow snapshot_dir to be a mountpoint.
+    - Search complete target tree for correlated subvolumes.
+    - Include snapshots from all mountpoints as candidates (disabled
+      due to uptream bug: github.com/kdave/btrfs-progs/issues/96).
+    - Always read /proc/self/mounts.
+    - Resolve realpath using readlink(1).
 
 btrbk-0.26.1