add async property to src/xml/XslTransform.js

[guest]

I should have provided this in the original version, so after some posts to the mail list I would like to get this into the src. Basically you can set the async property of a transformer. I have defaulted this to false so an XSL will be loaded before applying a transformation (I believe this to be the most common need). But, if you need an async load, then set the property to true. OK?

[dylan]

(In [7150]) fixes #2204, add async property to src/xml/XslTransform.js, cla on file

[guest]

It's pretty pointless to have a loadAsync parameter and to ignore it by always setting this.async=false. ;)