* src/roff/groff/groff.cpp (help), src/devices/grops/ps.cpp (usage),

* src/roff/groff/groff.cpp (help), src/devices/grops/ps.cpp (usage),
src/roff/troff/input.cc (usage): Updated.

* NEWS, doc/groff.texinfo: Updated.

* src/libs/libgroff/searchpath.cpp
(search_path::open_file_cautious): New function which also handles
`-' as stdin and stdout depending on the access mode.
* src/include/searchpath.h (search_path): Updated.

* src/devices/grops/ps.cpp (main): Handle new `-I' switch.
* src/devices/grops/ps.h: Include `searchpath.h'.
* src/devices/grops/psrm.cpp (resource_manager::supply_resource):
Open resource file with `include_search_path.open_file_cautious'.
* src/devices/grops/grops.man: Document new `-I' switch.

* src/devices/grodvi/dvi.cpp (main), src/devices/grolbp/lbp.cpp
(main), src/devices/grolj4/lj4.cpp (main),
src/devices/grotty/tty.cpp (main): Ignore new `-I' switch.

* src/preproc/soelim/soelim.cpp (include_list_length, include_list):
Replaced with...
(include_search_path): New global variable.
(include_path_append): Removed.
(main): Use `include_search_path.command_line_dir' to handle `-I'.
(do_file): Simplify, using new
`include_search_path.open_file_cautious'.

* src/roff/groff/groff.cpp (print_commands): Accept file handle as
parameter.
(main): Pass arguments to `-I' to both troff and devices.
Improve handling of `-V'.
* src/roff/groff/groff.man: Document changes to -I and -V.

* src/roff/troff/input.cpp (include_search_path): New global
variable.
(next_file, source, ps_bbox_request, transparent_file,
process_input_file): Use new
`include_search_path.open_file_cautious'.
(main) Handle `-I' switch.
* src/roff/troff/node.cpp (troff_output_file::really_copy_file):
Use new `include_search_path.open_file_cautious'.
* src/roff/troff/node.h: New extern symbol `include_search_path'.
* src/roff/troff/troff.man: Document new `-I' switch.