[gtk] (9 commits) ...Merge branch 'misc-multiselection' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  c3a6e35... Drop an unnecessary include (*)
  de6327a... multiselection: Clarify docs (*)
  8090e21... Add a test for multiselection persistence (*)
  fd7f19c... selectionmodel: Document the callback apis (*)
  b0cf7a9... Add a forgotten export (*)
  27ce68b... Add tests for select_callback (*)
  3e6e247... multiselection: Rewrite the select_callback implementation (*)
  e72c243... singleselection: Clarify docs (*)
  1567db1... Merge branch 'misc-multiselection' into 'master'

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