Fix problem with ellipses in .dt and with wrapping very short paragraphs

(1) ppgen temporarily transforms ellipses and some other special characters
into values that will not cause problems during processing, then it converts
them back into their real values near the end, just before writing the
output files. But for the .dt directive the reconversion at the end did not
occur, causing problems in the HTML title attribute.

(2) 3.42 had an error when wrapping very short "paragraphs" (one or two words)
that caused a Python exception.