Fixed a couple issues with parsing set-property op result

There are a couple issues being addressed int this commit. First,
the ModelEntityItemDef is not copied properly. It is missing
isExtensible and MaxNumValues variables. Second, the XmlV2String
writer and parser have mis-matched logic for processing ModelEntityItem.
Last thing was fixed is the wrong initialization of visibility for entityphrase.
Merge pull request #16 from yumin/master

Fixed a couple issues with parsing set-property op result