Replaced cat by message.

A message can be suppressed by suppressMessages. This replacement makes
it easier to turn off output.
Replace cat by warning.

Warnings are easier to locate in the output.
Added entry to changelog in file.
Changed cat to warning.

Warnings are easier to locate in the output.
Changed cat to message.

A message can more easily be suppressed in the output using
suppressMessages than cat.
Updated CHANGELOG.