internal/storetesting: more stringent AssertJSONCall test
Merge remote-tracking branch 'origin/v4' into 010-assertjson-lossless

Conflicts:
	internal/storetesting/http.go
Merge pull request #24 from rogpeppe/010-assertjson-lossless

internal/storetesting: more stringent AssertJSONCall test

This makes sure that *all* the data returned is as expected.