vpnc: Improve config completions

Load completions in /etc/vpnc by *.conf name, avoiding inclusion of
non-conf files from there as completions (e.g. vpnc-script). Also
support loading completions from explicit filenames elsewhere.

completions/vpnc

@@ -53,8 +53,19 @@ _vpnc()
     if [[ "$cur" == -* ]]; then
         COMPREPLY=( $( compgen -W '$( _parse_help "$1" --long-help )' \
             -- "$cur" ) )
+    elif [[ "$cur" == */* ]]; then
+        # explicit filename
+        _filedir conf
     else
-        COMPREPLY=( $( compgen -W '$( command ls /etc/vpnc )' -- "$cur" ) )
+        # config name, /etc/vpnc/<name>.conf
+        local IFS=$' \t\n' reset=$(shopt -p nullglob); shopt -s nullglob
+        local -a configs=( /etc/vpnc/*.conf )
+        configs=( "${configs[@]##*/}" )
+        configs=( "${configs[@]%.conf}" )
+        $reset
+        IFS=$'\n'
+        compopt -o filenames
+        COMPREPLY=( $( compgen -W '${configs[@]}' -- "$cur" ) )
     fi
 } &&
 complete -F _vpnc vpnc