Add option -G to .MPIMG to insert a gap between text and the image.
* tmac/www.tmac (www-finish-left-po, www-finish-right-ll,
www-finish-left-ll): Updated.
(www-image-just, www-image-gap, www-htmlimage-gap): New variables.
(MPIMG): Make option -L and -R optional.
Implement option -G.
* src/devices/grohtml/post-html.cpp
(html_printer::do_file_components): Don't use `stdout' as lvalue
since it can be a macro.
* src/libs/libgroff/strerror.c: Include errno.h to be in sync with
the corresponding test in aclocal.m4.