Add a --leaf-changes-only option to abipkgdiff

Add a --leaf-changes-only option to abipkgdiff

This patch adds the --leaf-changes-only option to abipkgdiff, just
like what we have for abidiff.  The patch also emit leaf changes
report by default when comparing two Linux Kernel packages.

The patch also adds the --impacted-interfaces and --full-impact
options.

	* doc/manuals/abipkgdiff.rst: Add documentation for the new
	--leaf-change-only, --impacted-interfaces and --full-impact
	options.
	* tools/abipkgdiff.cc (options::{leaf_changes_only,
	show_impacted_interfaces, show_full_impact_report): Add new data
	members.
	(options::options): Initialize them.
	(display_usage): Add help strings for the new --leaf-change-only,
	--impacted-interfaces and --full-impact|-f options.
	(set_diff_context_from_opts): Set the diff context for the
	'leaf-changes-only' and 'show-impacted-interfaces' flags.
	(parse_command_line): Parse the --leaf-change-only,
	--impacted-interfaces and --full-impact options.  Handle the case
	where the --linux-kernel-abi-whitelist|-w option is given a
	whitelist *package*.
	* tests/data/test-diff-pkg/spice-server-0.12.4-19.el7.x86_64-0.12.8-1.el7.x86_64-report-3.txt:
	New test output reference.
	* tests/test-diff-pkg.cc (in_out_spec): Compare
	data/test-diff-pkg/spice-server-0.12.4-19.el7.x86_64.rpm and
	data/test-diff-pkg/spice-server-0.12.8-1.el7.x86_64.rpm with the
	new --leaf-changes-only and --impacted-interfaces options, using
	the new output reference above.
	* tests/data/Makefile.am: Add the new test material to source
	distribution.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>