IsolatedStorageTarget - minor bug fixes

Minor fixes, enough to get the tests to pass.

- Check if a file exist before deleting, otherwise IsolatedStorageFile
will throw an error
- IsolatedStorageFile.MoveFile() doesn't throw an IOException, instead a
IsolatedStorageException
- Sequential archive internal dictionary didn't have the full name (Line
796)
Merge pull request #1 from joshgo/master

IsolatedStorageTarget - minor bug fixes