Windows 8 Storage fixes

[WaaghMan]

• Fixed BeginShowSelector / EndShowSelector not working.
• Fixed BeginOpenContainer / EndOpenContainer not working.
  ** Static variables added as a workaround for not being able to cast IAsyncResult to AsyncResult.
• Fixed StorageContainer methods throwing exceptions because there was no wait on the async methods.
• Fixed base path for StorageContainer
• Added a try/catch to StorageContainer.FileExists and StorageContainer.DirectoryExists
• Fixed OpenFile opening a Stream on the end of the file when the file existed.

[tomspilman]

We need someone that uses StorageContainer to give this a try.

[demonixis]

Hi,

I've tested it and it's work for save a file but when i'm try to loading datas i've this error

Exception de HRESULT : 0x80070005 (E_ACCESSDENIED

The problem seem to be in StorageContainer.cs line 515

[KonajuGames]

E_ACCESSDENIED usually happens when a stream has not been closed properly
when it was last used.

[mgbot]

Can one of the admins verify this patch?

[dellis1972]

@mgbot test

[tomspilman]

So another complication here. We just applied the branch migration plans:

https://github.com/mono/MonoGame/wiki/Branch-Migration-Strategy

So the develop3d branch will stop being updated and eventually deleted. So that leaves you with a choice here:

1. Close this PR and resubmit to the develop branch.
2. Let me merge it with develop3d, but there will be a delay of a few days before it is moved into develop.

Totally your call.

[WaaghMan]

Well, I'd go with 2 since it means less work for me :). Anyway the code should be fine, we're already using it on a game published on the Windows Store.