Upload new version fails with undefined index accept

[solsson]

error (code 8): Undefined index: accept

Since #20. We need to include upload new version in that use case.

[solsson]

Continuing from the test URLs in #20, these two should result in the form for the first existing extension:

• http://svn/svn/test/someimage?rweb=e.upload&accept=.gif,.png,.jpg
• http://svn/repos-web/edit/upload/?base=test&target=%2Fsomeimage&accept=.gif,.png,.jpg