Have the standard manpage header and footer print on every page of -Tps

Have the standard manpage header and footer print on every page of -Tps
output.  This is more tricky than you may think:  we can't just call the
header function out-of-state (i.e., before a flushln has occured)
because we'd clobber our current state.  Thus, we call at the beginning
and dump the output into an auxiliary buffer.

For the record, I don't think there's any other clean way to do this.
The only other Way That Works is to copy-aside *all* termp state, zero
it, and do the necessary headf/footf.  This is just as complex, as
memory needs to be alloc'd and free'd per margin.

Unfortunately, this prohibits page numbering (the margin is only printed
once), so I'll probably end up re-writing this down the line.