Obtain layer default style with original format

[giohappy]

Layer.default_style getter retrieve the style from Catalog.get_styles with recursive set to False (default value). This makes Catalog.get_styles the style name from styles.xml, without making a request for the detail XML for the style. The end result is that the Style object is created with style format sld10 independently from the original format,

If we want to keep the shallow retrieval of style for the Layer.default_style property we might consider implementing an explicit Layer.get_full_default_style() that will call (and set) the style using the recursive method.