tests: added RemoteStream to be able test non-local URLs offline

[milo]

No description provided.

[milo]

@dg Not sure you know that this @ mutes:

E_WARNING: stream_copy_to_stream(): RemoteStream::stream_stat is not implemented!
E_WARNING: stream_copy_to_stream(): RemoteStream::stream_read is not implemented!
E_WARNING: stream_copy_to_stream(): RemoteStream::stream_eof is not implemented! Assuming EOF

but stream_copy_to_stream() returns 0 after that.

[dg]

Error system in PHP is a tragedy…

I do not know how to distinguish between errors that lead to failure from those that are just informative. I can either throw an exception for any error like here or throw an exception on failing return value and remove @, so it will trigger warnings even exception will be catched.

possible solution: #94