Patch for #1794 (No file browsing in Darcs repos)
Before calling the darcs scm adapter, darcs needs the revision number being translated to the scmid. This was working for the entries(), diff() and fetch_changesets() methods. I added this for entry() and cat() in a similar fashion.
Starting from version 2.0.0, darcs supports listing the contents of a file in the repository. I added the code to read the version number and the cat() method (similar to what is there for subversion).
These were my first ruby lines - I hope I didn't screw up ... I'd be happy to see them upstream. Thanks for the great application!