setspace adjustments of \parskip and \footins

[davidcarlisle]

Issue #1 shows the package loses the stretch components of the math display skips by multiplying \bselineskip by a numeric factor.

Checking \parskip and \footins they have the same issue except that the following test inserted in 2011 appears to be inverted and so they are not adjusted at all in LaTeX2e:

% RF: 2011-12-19: only redefine \@setsize if under 2e; there have been
% reports of ltx209 packages failing when run with setspace under
% ltx2e, with this definition
\@ifundefined{NeedsTeXFormat}{%
\def\@setsize#1#2#3#4{%
  % Modified 1993.04.07--GDG per KPC
  \@nomath#1%
  \let\@currsize#1%
  \baselineskip #2%
  \baselineskip \baselinestretch\baselineskip
  \parskip \baselinestretch\parskip
  \setbox\strutbox \hbox{%
    \vrule height.7\baselineskip
           depth.3\baselineskip
           width\z@}%
  \skip\footins \baselinestretch\skip\footins
  \normalbaselineskip\baselineskip#3#4}%
}{}%

Changing this is likely to have a large effect on the spacing of existing documents especially if they have non zero parskip, as parskip will get scaled.

In any case \@setsize should probably be kept as the legacy wrapper around \@setfontsize and \@setfontsize adjusted if necessary. The definition here would lose the test on \protect in the current kernel definition, if it was activated.

@FrankMittelbach any thoughts on what we could do with this code?