maint: Add support for .ctags.d

Depending on the way ctags was compiled, it may look for
.ctags.d/*.ctags files rather than .ctags for reading configuration.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>
Acked-by: NMichal Privoznik <mprivozn@redhat.com>

.ctags.d/libvirt.ctags

+../.ctags
\ No newline at end of file