Log Message:
Changes 2.12.5:
* Documentation:
  - Show stock icon images in the API reference again.
  - Show some pictures of widgets in the API reference.
* Build:
  - Fix header inclusion and use using directive for C functions to
    fix build on gcc-4.3 (pre-releases) and Solaris.
  - Install and find all needed files for gtkmm-demo, and correct the
    executable name.