Correct the Bash completion script behaviour.

Correct the Bash completion script behaviour.

* wip/issue/bash-completion:
  Document in the changelog the ‘dcut’ completion improvement.
  Install the script for ‘dcut’ command completion.
  Add Bash script for completion of ‘dcut’ command.
  Document in the changelog the ‘dput’ completion improvements.
  Construct the set of options as a Bash array.
  Apply completion options only when appropriate for the case.
  Construct the values for ‘--delayed’ by a sequence expression.
  Use correct idiom to specify current word for matching.
  Correct the completion glob for source control files.
  Signature files are not input to the command; remove the attempt to match.
  Execute search for hostnames once, across all config files.
  Define cases with the conventional order for options spellings.
  Remove a superfluous conflation of separate collections.
  Migrate from deprecated completion helper function.
  Remove superfluous declarations of local variables.
  Properly quote values that could contains special characters.
  Standardise bash-completion continuation and indentation.
  Move ‘dput’ Bash completion to a script explicitly named for the command.