While seeking, metadata must not be updated.  ResponseBoundary() was
added in MPD 0.19.1, but I forgot to add the IsSeeking() check there.
This caused the "seekable" flag to reset.

Fixes playback of redirected streams.

Make the "open" method of plugins "file" and "archive" dummy methods
that always fail.  Instead, let InputStream::Open() hard-code access
to these two plugins by using OpenLocalInputStream().  This allows
simplifyin the algorithm for falling back to probing archive plugins.

This special case was useless.  Fixes the dreaded "Unrecognized URI"
error message when a file does not exist.

The second time init was called, http_200_aliases pointed to a freed pointer
and leaded to a SEGFAULT.

Fixes hanging NFS client.

Generate more detailed error messages.

Eliminate duplicate definition (in input plugin and decoder plugin).

Avoids off-by-one bug and obsoletes the bug fix in commit 966c4244

More robust and cancellable.

New base class for other InputStream implementations that run in the
I/O thread.

Fixes assertion failure.

Remove the "whence" parameter that is not actually necessary, and only
complicates the InputStream implementations.

Caused by commit 0b4fa41a

Make attributes const, don't allow partial initialization.
Instantiate the CdioParanoiaInputStream object at the end of
input_cdio_open().