Server "BAD" response when we fetch message summaries

Hi Jeff,

I have a little issue using `IFolder.Fetch` method.
It only occurs when we have as parameter :
````csharp
    MessageSummaryItems.All
    MessageSummaryItems.Full
    MessageSummaryItems.Fast
````

e.g. : `inbox.Fetch(0, -1, MessageSummaryItems.All, cancel.Token);`

I've take a look on [RFC 3501](http://tools.ietf.org/html/rfc3501#section-6.4.5), no answer...

But after debugging my app it appears that the Exception was raised due to the parenthesis around "ALL", "FAST" & "FULL" arguments. 
No errors for "BODY"

My pull request fix that, I've tested this fix with 2 of my mailboxes and with all overrides of `IFolder.Fetch` method