Log Message:
xfce4-conf: update to 4.16.0

Change log:

4.16.0
======
- Don't use shebang for bash completion file
- Remove GLIB_CHECK_VERSION IFDEFs which are obsolete after glib bump
- bump glib (and gio, gthread, etc) minimum to 2.50.0
- remove last traces of xfconf-perl
- Fix make distcheck and enable it on gitlab CI
- Add README.md to EXTRA_DIST
- Post release autoconf git revision

4.15.1
======
- Fix stray double-quote in bash-completion PKG_CONFIG invocation
- Disable parallelism on all tests
- Adds new README.md and updates AM_INIT_AUTOMAKE
- xfconf-cache: Fix access to freed data (#16)
- Translation Updates: oc, he, hu, hy_AM, lt, sk, sq, ug, tr.

4.15.0
======
- Implement custom test driver
- Use 'gsettings' as a common channel name for the GSetting backend
- Bug #14789 Fix GSettings backend assertion error, when probed but not used
- Enable GSettings backend build by default
- Add Bash completion for xfconf-query
- Bug #15960: Add some missing xfconf_shutdown() in xfconf-query
- Bug #15951: Fix 'xfconf_get_error_quark' introspecting warning
- Remove perl bindings
- Fix vala binding in dist tarball
- Translation Updates: be, da, el, es, he, hr, hu, hye, gl, nl,
  sl, sq, zh_CN, zh_HK, zh_TW