nested calls to Chunk.map never return

Nobody has claimed this yet.

It seems that map does not work when called on an already mapped chunk.

For example, this code will never execute the dust.render callback:

``` javascript
dust.loadSource(dust.compile("test of async mapping {x}", "test"));
var data = {
x : function(chunk) {
return chunk.map(function(chunk2) {
var f2 = function() {
chunk2.write("hmmm!");
// change the next line to chunk.map and it works as expected
chunk2.map(function(chunk3) {
var f3 = function() {
chunk3.write("mmm!!");
chunk3.end();
};
setTimeout(f3, 1000);
});
chunk2.end();
};
setTimeout(f2, 1000);
});
}
};
dust.render("test", data, function(err, out) {
$("body").html(out);
});

```

Is this a limitation, a bug, or am I doing something horrible?

Start by locating the Chunk.map implementation and any existing tests for nested or asynchronous mapping. Reproduce the supplied example, trace the nested callback and completion behavior, and consider the issue done when nested Chunk.map calls complete and the dust.render callback receives the rendered output.

Written by the indexing model from the issue text.