Add support for bash autocomplete in main dindexer

I'm not sure this is something that should be in the code, since
compgen -W "delete locate navigate query scan" loc
would do just the same as
dindexer --printactions=loc
so this is a duplicated functionality. However this commit is
self-contained, so it should be easy to revert it, if needed.

dindexer_cmd_complete.sh.in

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+if [ "$3" == "@bare_name@" ]; then
+    exec @bare_name@ --printactions=$2
+fi