Release 2018.2

There are enough fixes here, and there are some potentially larger patches
incoming like wmanley's checkout speedups and the payload link that will need
soak time in master.

Closes: #1455
Approved by: jlebon

src/libostree/libostree-released.sym

@@ -454,6 +454,10 @@ LIBOSTREE_2017.15 {
 LIBOSTREE_2018.1 {
 } LIBOSTREE_2017.15;
 
+LIBOSTREE_2018.2 {
+  ostree_commit_get_content_checksum;
+} LIBOSTREE_2018.1;
+
 /* NOTE: Only add more content here in release commits!  See the
  * comments at the top of this file.
  */