#70 GraphML directed edges attribute wrong on write()

[Christian]

The write method of the GraphMLConverter class gets the directed schema information and then compares it with a "directed" string in order to write:
<graph edgedefault="[directed|undirected]">

It should expect a boolean value from the directed schema field, not a string, when:
var ed:Object = data.edges.schema.getFieldByName(DIRECTED).defaultValue;

So instead of:
graph.@[EDGEDEF] = ed==DIRECTED ? DIRECTED : UNDIRECTED;

It should do:
graph.@[EDGEDEF] = ed ? DIRECTED : UNDIRECTED;