Added `brp' request: This is p as a request.
* src/roff/troff/env.cc (environment::do_break): Add parameter
`spread'.
(do_break_request): New function (was `break_request').
(break_request): Calls `do_break_request'.
(break_spread_request): New; calls `do_break_request'.
(init_env_requests): Updated.
* src/roff/troff/env.h: Updated.
* NEWS, src/roff/troff/troff.man, man/groff.man: Document it.
* VERSION: Increased to 1.17.1.
* tmac/an-old.tmac: Fix minor compatibility mode issue.
* tmac/troffrc-end: Make it really work in compatibility mode.