server/upsd.c: set_exit_flag(): sig is not UNUSED

configure.ac: cut the release of NUT v2.8.0

docs/nut-qa.txt: mention "make check-NIT-devel" helper target

docs/FAQ.txt: add more reasons and symptoms that a running driver dis…

…appears

Merge pull request networkupstools#1345 from jimklimov/doc-netbsd

Doc for netbsd builds, more clang 13 support, more manpage related recipes

“v2.7.4”

Release 2.7.3

NUT 2.7.2 (signed)

NUT v2.7.2

Modify version in configuration descriptor.