Background buffering and better timeout handling.  This patch sort of
obsoletes the input_plugin method buffer().

Assume the flag is true when the "easy" CURL handle is NULL.  That
way, we don't need to keep track if CURL has sent us the "DONE"
information yet.

Release it immediately when end-of-file has been reached.  We don't
need that handle anymore, because the rest is delivered from the
buffers.

Allow closing the handle while preserving the remaining buffers.

Remove a cast.

Let the caller know what happened, he's responsible for logging.

This function initializes global variables.

libsoup uses GType.

To demonstrate the new I/O thread.  libsoup is well-integrated into
the GLib main loop, which made this plugin pretty easy to write.

As a side effect, we have to initialize the I/O thread in all debug
programs that use the input API.

Try to eliminate the remaining blocking I/O.

Eliminate duplicate code.

Better than dereferencing NULL.

No point in returning true, and checking that.

.. and not -1, which is "true".

Allocate objects on the stack to reduce heap overhead.

Not unsigned char.  Eliminate useless casts.

Only used internally.

This defaults to "false" when the method pointer is NULL.

Check if the stream is suspended; wake up the main loop when it
becomes suspended.

Not a bool.

Unlock the mainloop in all code paths.