Improve Debian bash-completion support

* Autoconf queries pkgconf for bash-completion dir-- resolves
  lintian's `package-install-into-obsolete-dir` diagnostic
* Use improved completion snippet from
  <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=782169>
* Remove old /etc/bash_completion.d/mosh "conffile" with
  dh-maintscript + dpkg-maintscript-helper

Closes #628.

Signed-off-by: John Hood <cgull@glup.org>

conf/Makefile.am

@@ -1,3 +1,5 @@
+completionsdir = @completions@
+dist_completions_DATA =
 nobase_dist_sysconf_DATA =
 
 if INSTALL_UFW
@@ -5,5 +7,5 @@ if INSTALL_UFW
 endif
 
 if INSTALL_COMPLETION
-  nobase_dist_sysconf_DATA += bash_completion.d/mosh
+  dist_completions_DATA += bash-completion/completions/mosh
 endif

conf/bash-completion/completions/mosh

@@ -0,0 +1,9 @@
+_mosh () {
+    local cur prev
+
+    _init_completion || return
+
+    _known_hosts_real -a "$cur"
+}
+
+complete -F _mosh mosh

conf/bash_completion.d/mosh

@@ -1 +0,0 @@
-complete -F _known_hosts mosh