[gegl] (5 commits) Non-fast-forward update to branch wip/tile-read-lock

[Ell <ell src gnome org>]

The branch 'wip/tile-read-lock' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  6a8a0dc... buffer: add gegl_tile_read_{lock,unlock}()
  5ab4fd1... buffer: use gegl_tile_read_{lock,unlock}() when reading til

Commits added to the branch:

  bfc3283... tests: Prevent parallel make check (*)
  4161757... buffer: fix empty tile uncloning rollback (*)
  4af8785... buffer: eliminate empty mipmapped tile generation; fix pote (*)
  f5a0f3a... buffer: add gegl_tile_read_{lock,unlock}()
  9b0976a... buffer: use gegl_tile_read_{lock,unlock}() when reading til

(*) This commit already existed in another branch; no separate mail sent