Usage: all text included in between
%    \comment ... \endcomment
% or \begin{comment} ... \end{comment}
% is discarded. The closing command should appear on a line
% of its own. No starting spaces, nothing after it.
% This environment should work with arbitrary amounts
% of comment.
%
% Other 'comment' environments are defined by
% and are selected/deselected with
% \includecomment{versiona}
% \excludecoment{versionb}
%
% These environments are used as
% \versiona ... \endversiona
% or \begin{versiona} ... \end{versiona}
% with the closing command again on a line of its own.
%
% Basic approach:
% to comment something out, scoop up  every line in verbatim mode
% as macro argument, then throw it away.
% For inclusions, both the opening and closing comands
% are defined as noop