FIX issue 996.
Ruby 1.9.3 no longer had .id method for the Object class. Changed calls for
repository files and directories (which inherited it from id) to use
object_id instead because it is still available in 1.9.3
Merge pull request #976 from umsmit32/issue-966

Closes #966 Files added on submission page are not displayed.

When you add a file as a student on the submission page, the file doesn't show up in the list. On other pages it says you have uploaded a file but you can't see it.

This issue only occurs in ruby version 1.9.3 and not 1.8.7.