Access 'file' view for a blob hash directly

[GoogleCodeExporter]

This is related to issue 7, but slightly different. Issue 7 enables:
  https://..../path/to/repo/+/<ref>/path/to/blob?format=TEXT

It would also be extremely awesome to be able to do (e.g.):
  https://..../path/to/repo/+blob/<hash>?format=TEXT  # OR
  https://..../path/to/repo/+/<hash>?format=TEXT

IIUC, the naive permission checks for this would be really gnarly, because 
you'd have to walk all accessible refs until you hit a commit with a tree (or a 
chain of trees) which eventually contained the blob.

Talking to dborowitz, however, it seems like it might be possible to re-use the 
object reachability calculation which is normally done on a clone to do this 
check. The object set calculation is apparently implemented with super-fast, 
bitmap-accelerated hyper-algorithmic goodness :).

Original issue reported on code.google.com by [email protected] on 29 May 2014 at 10:54