Replace usage of the JDK7 java.nio.file.OpenOption by our own CodeList for the following reasons:
- While java.nio.file.OpenOptions are mostly the same than the DataStore OpenOption for now,
  we have no guaranteed that it will still be the case in the future.
- Sharing the same OpenOption between file and DataStore would allow to pass DataStore-specific
  OpenOption to java.nio.file, or java.nio.file-specific OpenOption to DataStores. It may not
  really hurt since java.nio.file ignores unknown options, but it nevertheless may increase the
  risk of confusion.
- java.nio.file is JDK7 specific while we still have a JDK6 branch.


git-svn-id: https://svn.apache.org/repos/asf/sis/branches/JDK7@1509040 13f79535-47bb-0310-9956-ffa450edef68