[TypeScript] Prevent the cs.d.ts to be generated twice

[IntellisenseParser](https://github.com/madskristensen/WebEssentials2013/blob/master/EditorExtensions/Misc/CodeGeneration/IntellisenseParser.cs) and the [ScriptIntellisenseListener](https://github.com/madskristensen/WebEssentials2013/blob/master/EditorExtensions/Misc/CodeGeneration/ScriptIntellisenseListener.cs) share the same code listening to the change on the file. This cause the C# class to be generated in typescript (or javascript) twice.
Put a breackpoint [here](https://github.com/madskristensen/WebEssentials2013/blob/master/EditorExtensions/Misc/CodeGeneration/IntellisenseWriter.cs#L21) and save the .cs file

This will help the performance on large files (https://github.com/madskristensen/WebEssentials2013/issues/922)