due to unconditional use of .ne. groff apparently inserts some virtual trap
at the end of each page, and this was causing the .ne commands to output extra
lines. Solution is to only use them in troff.
Also fix a related bug in .It, where it would insert a page break in the middle
of a sentence.
Remove the end of page trap in nroff mode, as this causes .sp to sometimes eat
the space due to the nearby trap.
Lastly, undue a previous change that broke the formatting of the SYNOPSIS
section, until we determine the right way to fix that.
