Before this, a stream error would not be readable by user code, as the
`recv_features()` function would not even attempt to parse it. This
change allows application code to react to stream errors which are
received before stream features are received.
skip-changelog, because there's no release with the xmlstream module
yet.
This allows to detect and handle dying streams without getting stuck
forever.
Timeouts are always wrong, though, so we put the burden of choosing the
right values (mostly) on the creator of a stream.
