Bugs in libroar which broke the MPD build have been annoying me for
quite some time, and the newest bug has now hit my main build machine:

 https://github.com/MusicPlayerDaemon/MPD/issues/377

Problem is the usage of the typedef `_IO_off64_t` in libroar's
`vio_stdio.h`:

 int roar_vio_to_stdio_lseek (void *__cookie, _IO_off64_t *__pos, int __w);

This `_IO_off64_t` is an internal implementation detail of glibc and
was removed in version 2.28.  Nobody must ever use it.  Why the ****
did the RoarAudio developers use it?  Not using internal typedefs
isn't exactly rocket science.

This annoys me enough to finally remove the plugin.  Anyway, I've
never heard of anybody using RoarAudio, so my best guess is that
nobody will notice.

So long, autotools!  This is my last MPD related project to migrate
away from it.  It has its strengths, but also very obvious weaknesses
and weirdnesses.  Today, many of its quirks are not needed anymore,
and are cumbersome and slow.  Now welcome our new Meson overlords!

GCC 6.3.0 emits bogus warnings like this:

 In file included from src/lib/dbus/UDisks2.cxx:22:0:
 src/lib/dbus/ReadIter.hxx: In instantiation of 'ODBus::ReadMessageIter::ForEachProperty(F&&)::<lambda(auto:2&&)> [with auto:2 = ODBus::ReadMessageIter; F = std::_Bind<void (*(std::reference_wrapper<UDisks2::Object>, std::_Placeholder<1>, std::_Placeholder<2>))(UDisks2::Object&, const char*, ODBus::ReadMessageIter&&) noexcept>]':
 src/lib/dbus/ReadIter.hxx:102:6:   required from 'ODBus::ReadMessageIter::ForEachRecurse(int, F&&)::<lambda(auto:1&&)> [with auto:1 = ODBus::ReadMessageIter&; F = ODBus::ReadMessageIter::ForEachProperty(F&&) [with F = std::_Bind<void (*(std::reference_wrapper<UDisks2::Object>, std::_Placeholder<1>, std::_Placeholder<2>))(UDisks2::Object&, const char*, ODBus::ReadMessageIter&&) noexcept>]::<lambda(auto:2&&)>]'
 src/lib/dbus/ReadIter.hxx:92:5:   required from 'void ODBus::ReadMessageIter::ForEach(int, F&&) [with F = ODBus::ReadMessageIter::ForEachRecurse(int, F&&) [with F = ODBus::ReadMessageIter::ForEachProperty(F&&) [with F = std::_Bind<void (*(std::reference_wrapper<UDisks2::Object>, std::_Placeholder<1>, std::_Placeholder<2>))(UDisks2::Object&, const char*, ODBus::ReadMessageIter&&) noexcept>]::<lambda(auto:2&&)>]::<lambda(auto:1&&)>]'
 src/lib/dbus/ReadIter.hxx:101:3:   required from 'void ODBus::ReadMessageIter::ForEachRecurse(int, F&&) [with F = ODBus::ReadMessageIter::ForEachProperty(F&&) [with F = std::_Bind<void (*(std::reference_wrapper<UDisks2::Object>, std::_Placeholder<1>, std::_Placeholder<2>))(UDisks2::Object&, const char*, ODBus::ReadMessageIter&&) noexcept>]::<lambda(auto:2&&)>]'
 src/lib/dbus/ReadIter.hxx:114:3:   required from 'void ODBus::ReadMessageIter::ForEachProperty(F&&) [with F = std::_Bind<void (*(std::reference_wrapper<UDisks2::Object>, std::_Placeholder<1>, std::_Placeholder<2>))(UDisks2::Object&, const char*, ODBus::ReadMessageIter&&) noexcept>]'
 src/lib/dbus/UDisks2.cxx:71:30:   required from here
 src/lib/dbus/ReadIter.hxx:114:53: error: declaration of 'ODBus::ReadMessageIter&& i' shadows a parameter [-Werror=shadow]
    ForEachRecurse(DBUS_TYPE_DICT_ENTRY, [&f](auto &&i){
                                                      ^
 src/lib/dbus/ReadIter.hxx:101:33: note: shadowed declaration is here
    ForEach(arg_type, [&f](auto &&i){
                                  ^

Since nfs_stat_async is deprecated.

This is the version in Debian Jessie (oldstable).

Required according to RFC 3986:

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

Closes #330

This way, IsFileNotFound() can detect status 404.

Allows callers to extract the NFS error code.

Documentation will follow soon.