docs/parse-support-md: Do caveats properly (!)

docs/parse-support-md: Do caveats properly (!)

Each document has its own objects in @insections.  Only the first
RealSect encountered ends up in the main $toplevel_sectlist tree.

This means that trying to unify the Caveats information for all
version in the RealSect (the $insection) does not work.  The caveats
for all versions that aren't the first one where this section was seen
end up in the @insections array during parsing of that version, but
not recorded in the main tree.

The result was that footnotes would only appear in the output for
versions which were the most recent version where that feature row or
category appeared.  The other footnotes would be lost.

Instead, store HasCaveat in the sectnode.  That means ri_Para needs to
find the sectnode.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>