* Creates a #EvDocument for the document at @uri; or, if no backend handling
* the document's type is found, or an error occurred on opening the document,
* returns %NULL and fills in @error.
* Creates a #EvDocument for the document at @uri; or, if no backend handling
* the document's type is found, or an error occurred on opening the document,
* returns %NULL and fills in @error.