* src/devices/grohtml/html-text.cpp (html_text::do_pre): Preserve
paragraph spacing.
(html_text::done_para): Unset `start_space'.
(html_text::remove_para_align): Call `retrieve_para_space' for the
spacing.
* src/devices/grohtml/post-html.cpp (html_printer::emit_raw): Unset
`seen_space'.
(html_printer::do_check_center): Emit vertical space if necessary.
* src/roff/troff/env.cpp (environment_switch): Preserve
`seen_space', `seen_eol', and `suppress_next_eol' while switching
environments.
* src/roff/troff/node.cpp (suppress_node::suppress_node): Set
`is_special'.