Found with modernize-use-override
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Fix src/ls.cxx to only print unique schemas.
Refactor src/ls.cxx to use src/input/InputPlugin functionality.

Add dynamic enumeration support to curl plugin.

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

Required according to RFC 3986:

> An implementation should accept uppercase letters as equivalent to
> lowercase in scheme names

Closes #330

This adds a bit of overhead, but also adds flexibility to the API,
because arbitrary triggers may be invoked from that virtual method
implementation, not just Cond::signal().

The motivation for this is to make the handlers more dynamic, for the
upcoming buffering class utilizing ProxyInputStream.

Eliminate dependency on io_thread_get().

Make sure we're using the same EventLoop as the NfsManager.

Eliminate dependency on io_thread_get().

The old struct config_param remains only for top-level string options.

Fixes hanging NFS client.

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

More robust and cancellable.

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