Consider using repository for page existence checks
Currently Hatta checks page existence by directly looking if the file exists. Even if the file is not tracked by the repository, it's considered existing if the file is there. This was done for efficiency reasons -- checking for page existence is a common action and the repository access may be slow... But it was never actually verified. It may as well happen that checking whether a file is tracked in an already opened repository is actually faster. This has to be tested.