Release 2019.4

Tiny release. Just want to get out the important bugfixes instead of
backporting patches (notably the gpg-agent stuff and
`ostree-finalize-staged.service` ordering).

Closes: #1927
Approved by: cgwalters

src/libostree/libostree-released.sym

@@ -571,6 +571,10 @@ global:
   ostree_kernel_args_to_string;
 } LIBOSTREE_2018.9;
 
+LIBOSTREE_2019.4 {
+  ostree_repo_mark_commit_partial_reason;
+} LIBOSTREE_2019.3;
+
 /* NOTE: Only add more content here in release commits!  See the
  * comments at the top of this file.
  */