completion/bash: add completion rules for ctags

Close #1168.

The changes for Makefile.am and configure.ac are derrived
from util-linux. Their licenses are covered withn "The ./COPYING file (GPL-2.0-or-later)".

Quoted from README.licensing:

    The project util-linux doesn't use the same license for all of the code.
    There is code under:

       * GPL-3.0-or-later   - GNU General Public License version 3, or any later version

       * GPL-2.0-or-later   - GNU General Public License version 2, or any later version

       * GPL-2.0            - GNU General Public License version 2

       * LGPL-2.1-or-later  - GNU Lesser General Public License 2.1 or any later version

       * BSD-3-Clause       - BSD 3-Clause "New" or "Revised" License

       * BSD-4-Clause-UC    - BSD 4-Clause University of California-Specific

       * Public Domain

    Please, check the source code for more details. A license is usually at the start
    of each source file.

    The ./COPYING file (GPL-2.0-or-later) is the default license for code without
    an explicitly defined license.

Author: masatake

Makefile.am

@@ -278,3 +278,9 @@ dist-hook:
 include $(top_srcdir)/makefiles/testing.mak
 
 include $(top_srcdir)/makefiles/help.mak
+
+bashcompletiondir = @bashcompletiondir@
+if BASH_COMPLETION
+dist_bashcompletion_DATA  =
+dist_bashcompletion_DATA += completion/ctags.bash
+endif