[gtk/matthiasc/for-master] (10 commits) ...bitset: Add more tests

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  6a4b5ea... Annotate nullable argument (*)
  24d6a19... Add pre-condition check on nullable argument (*)
  117c71f... Merge branch 'issue-2900' into 'master' (*)
  608cbc2... printeditor: Cosmetics (*)
  6774f36... print-editor: Allow opening files (*)
  59fe4a3... printeditor: Add desktop file and appdata (*)
  0c9a0df... Merge branch 'print-editor' into 'master' (*)
  c4b2112... Merge branch 'matthiasc/for-master' into 'master' (*)
  02d4d3e... bitset: Correct preconditions in gtk_bitset_add_rectangle
  370fb5e... bitset: Add more tests

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