I brokez the NetKAN. This fixes it.

Apparently the content-type is provided by the browser, so really it
could be anything for a zip file. We now check a couple more types, and
assume a `.zip` extension is also good.

I'm really sorry. This is why I should write more tests.
CKAN.dll: Greatly simplified NetCache operaiton.

- NetCache no longer requires a temp dir.
- No longer move files by default.
- Fixed serious bug where our generated hashes could contain slashes.
- NetCache is now file transaction aware.
Merge branch 'bugfix_i_broke_netkan' into netcache

* bugfix_i_broke_netkan:
  I brokez the NetKAN. This fixes it.
Tests/NetCache: Show presence of double-store bug.