tr: .fl request

It is just an alias for .br to cause an implicit line break.
Reported by Carsten Kunze <carsten.kunze@arcor.de>.
ren: requests causing line breaks should output the first page

Reported by Carsten Kunze <carsten.kunze@arcor.de>.
ren: assigning \n% should set the next page number

Unless the next page number is set with .pn X or .bp X.
ren: .sp inside diverted text should not be inhibited after .ns

Reported by Carsten Kunze <carsten.kunze@arcor.de>.
ren: eject the first page after triggering the trap at page top

Reported by Carsten Kunze <carsten.kunze@arcor.de>.