test: don't run downstream caching test with native fetcher
native-fetcher: fix to work with nginx 1.5.8+

nginx 1.5.8 changed the resolver api, which the native fetcher uses.

Fixes #578.

Squash-merge of @dinic's #581.
native-fetcher: support non-GET request methods like PURGE
trunk-tracking: update from r3677 to r3696.

Add inline unauthorized resources test and fix rendered image dimensions test.