File Upload Fixes

Dunno why this was buggered again. ":back" doesn't seem to function as it used to.
Also, when uploading a file from page "foo", it's important to return to "foo" after
a successful upload, rather than redirecting to the HomePage.

Finally, a favicon tweak.

app/controllers/file_controller.rb

app/views/file/file.rhtml

public/favicon.ico

test/functional/file_controller_test.rb

vendor/rails/actionpack/lib/action_controller/response.rb