Return empty string from list import.

The documentation never said that a list was returned; indeed the example
provided is broken in that it prints out ARRAY(...) if run. Let us change
its behaviour to do as expected by the docs.

Changes

@@ -10,6 +10,10 @@
 #
 #========================================================================
 
+* Matthew Somerville stopped a list import from printing an ARRAY(...) string.
+  https://github.com/abw/Template2/issues/33
+
+
 #-----------------------------------------------------------------------
 # Version 2.27 - 13th December 2016
 #------------------------------------------------------------------------

lib/Template/Manual/VMethods.pod

@@ -552,7 +552,7 @@ current list.
        two   = [ 4 5 6 ];
        three = [ 7 8 9 ];
        one.import(two, three);
-       one.join(', );     # 1, 2, 3, 4, 5, 6, 7, 8, 9
+       one.join(', ');     # 1, 2, 3, 4, 5, 6, 7, 8, 9
     %]
 
 =head2 merge

lib/Template/VMethods.pm

@@ -616,7 +616,7 @@ sub list_unique {
 sub list_import {
     my $list = shift;
     push(@$list, grep defined, map ref eq 'ARRAY' ? @$_ : undef, @_);
-    return $list;
+    return '';
 }
 
 sub list_merge {

t/vmethods/list.t

@@ -286,7 +286,8 @@ Tom
 -- name list import one --
 [% list_one = [ 1 2 3 ];
    list_two = [ 4 5 6 ];
-   list_one.import(list_two).join(', ') %]
+   list_one.import(list_two);
+   list_one.join(', ') %]
 -- expect --
 1, 2, 3, 4, 5, 6
 
@@ -295,7 +296,8 @@ Tom
 [% list_one = [ 1 2 3 ];
    list_two = [ 4 5 6 ];
    list_three = [ 7 8 9 0 ];
-   list_one.import(list_two, list_three).join(', ') %]
+   list_one.import(list_two, list_three);
+   list_one.join(', ') %]
 -- expect --
 1, 2, 3, 4, 5, 6, 7, 8, 9, 0