doc: Ship Docbook's callout images.

Dependencies

• [2] 6U6KBFYP Build the HTML manual; add the HTML & PDF to the distribution; install them.
• [*] FV2M6MOT hydra: use autoconf/-make

Change contents

• edit in doc/manual/Makefile.am at line 18
  [2.500]

  [2.500]
  + # Embed Docbook's callout images in the distribution.

  + EXTRA_DIST = images

  +