Move yadis discover test data to the test case.
Split yadis discovery tests into two test cases for successes and failures.
Extract failure-related part of discoverdata.generateResult and inline it into the test itself.
Use support.urlopen for Failure test.

- Remove tests for 404 with headers and body it is now an exception
  instead of a response so the code can't analyze it anyway.
No need to test two different error codes doing the same thing.
Merge two special yadis discovery tests.
Removed unreachable branch in Discover.
Split X-XRDS-Location tests into a separate test case.
Removed redirection tests in test_yadis_discover. This is no place to test urlopen.
Moved lowercase header test into YadisLocation
Split XRDS + bad content type test into specials.
Use support.urlopen for direct XRDS discovery tests.
Removed discoverdata.

- Removed discoverdata.py
- Removed remains of test1-discover.txt
- Removed a custom fetcher from test_yadis_discover.py
Renamed YadisLocation to Location.
Keep only the normalized uri on DiscoveryResult
Call yadis discover recursively until an XRDS found.

- usedYadisLocation is constant False now
Merge direct and location-based yadis discovery tests.
Removed unused usedYadisLocation
Don't keep content_type on DiscoveryResult as its type is determined by parsing.
Remove unreachable condition from whereIsYadis.

The function is now called only if discover() decided that the
document is not XRDS, so no need to check for it again.