Import Entr 5.6 new upstream release

See commits for details.

± git log --first-parent --graph --format='format:%C(yellow)%h%C(reset) %s'

• e32ac5de Patch upstream system tests able to run without a tty
• c0f92c6e Patch system test to be able to test the installed 'entr' binary
• af42b766 Drop kFreeBSD patches which are no longer properly maintained/tested
• a6feef8e Add 'gawk' to autopkgtest dependencies
• 4daf468a Bump standards version to 4.7.0 and use new pkgconf name as dependency
• 72d2e37c Update changelog and refresh patches after 5.6 import
• 9662d8f8 Update upstream source from tag 'upstream/5.6'

Before this is merged and finalizes, ideally also !5 (merged), !6 (merged) and !8 (merged) would be reviewed and merged.

Import was done using all features available in git-buildpackage, linking together the upstream release tag, the upstream tarball import and also using pristine tar. For reference, see gitk visualizations:

Test builds at https://launchpad.net/~otto/+archive/ubuntu/ppa/+builds?build_text=&build_state=all passed on all architectures: