[WF4] Tests for Bookmark support and the effect of BookmarkOptions.

-Testing effect of the BookmarkOptions specified for bookmarks on
  -Resumption of bookmarks
  -Workflow runtime state (eg causing idle status)
  -Implicit / explicit removal of bookmarks
-Note: Tests show NativeCallbackActivityContext may not be necessary -
seems validation should take place in ScheduleActivity(act, cb) method,
throwing error if Delegate.Target is null and context param is accessed by
implementing method body. Check by reflection?
-Some additional bookmarking related tests
-Some other tidying