2.3.23

This release is all build system mods, trying to get a reasonable package for RHEL 7 that builds under Koji.

• Build: silence CC lines, fix AC_LANG_CONFTEST warnings, fix $(EXEEXT)
  warnings.
• Build: install System V init scripts if --with-systemdsystemunitdir
  is not configured and include both in EXTRA_DIST.
• Build: re-enable 'make check' unit tests.
• Build: fix some 'make distcheck' issues, but until unit tests are fixed
  to find *.exp and *.conf files in $(srcdir), this will still fail.
• RPM: configure genders, httppower, snmppower, and tcp-wrappers
  unconditionally; update URL.