hang footnotemarks in white space after a dropchar on the line
the dropchar begins.
fix width of text column after hanging footnote after a dropchar
hang both footnotes and punctuation in whitespace following drop
char on the line the dropchar is defined.
generalise left hang check.
make thin spaces non-elastic.
attempt in vain to stop '\,'' spliting over lines.
fix hanging of footnotes over punctuation in right margin
fix calculation of line width when footnotes hang over punctuation.