Just like what abidiff does, this patch avoids emitting redundant diff
report messages unless the user provides the --redundant switch.
* tools/abipkgdiff.cc (options::show_redundant_changes): New data
member.
(options::options): Initialize it.
(display_usage): Add a help string for the --redundant command
Line option.
(set_diff_context_from_opts): New static function.
(compare): Take the options variable. Set the diff context from
the options, especially if we should show redundant changes or
not. Use that diff context when comparing ABIs.
(parse_command_line): Parse the new --redundant command line
switch.
* doc/manuals/abipkgdiff.rst: Document the new --redundant option.