When nesting for non-list contexts, inherit list info.

This ensures that if you enter a conditional block while inside a list
block, the list "state" from the outer list will still be visible. For
example (somewhat contrived, but gets the point across):

{{#list}}
{{#name}}{{-index}}. {{.}}{{/name}}
{{^name}}{{-index}}. No name!{{/name}}
{{/list}}

Yields something like:

1. Bob
2. Mary
3. No name!
4. Jim

Fixes #90.

src/test/java/com/samskivert/mustache/SharedTests.java

@@ -431,6 +431,23 @@ public abstract class SharedTests extends GWTTestCase
              context("things", Arrays.asList("foo", "bar", "baz")));
     }
 
+    @Test public void testNestedIndex () {
+        class Foo {
+            public String name;
+            public Integer quantity;
+            public Foo(String name, Integer quantity) {
+                this.name = name;
+                this.quantity = quantity;
+            }
+        }
+        String tmpl =
+            "{{#fooList}}\n" +
+            "{{#quantity}}|q{{-index}}={{quantity}}{{/quantity}}|{{name}}\n" +
+            "{{/fooList}}";
+        test("|q1=1|a\n|b\n", tmpl,
+             context("fooList", Arrays.asList(new Foo("a", 1), new Foo("b", null))));
+    }
+
     @Test public void testLineReporting () {
         String tmpl = "first line\n{{nonexistent}}\nsecond line";
         try {