The number of MPD installs on Android < 5.0 is negligible, and that
API version introduces lots of useful features for MPD.

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.

See commit be137a19

Fixes crash due to "pure virtual method called" in the "mms" input
plugin.  Closes #253

Without setting the "ready" flag, the caller will wait in WaitReady()
forever, locking up MPD.  Closes #252

Requires Android API 21, but we want to support older versions as
well.

Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

InputStream::Read() and InputStream::Seek() are called with the mutex
locked.  That means the implementation must not block, or unlock the
mutex before calling into blocking code.

Previously, a slow CD drive could stall the whole MPD process,
including the main thread, due to this problem.

Closes #149

It's not possible to set CURL options after curl_easy_perform(), and
thus the CURLOPT_RANGE had no effect.

From the CURLOPT_RANGE documentation: "The application does not have
to keep the string around after setting this option."

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

Fixes a GCC warning because %llu appears to be unsupported by the
Windows standard library.

Yet another potential crash bug fix.

Doesn't make a practical difference - but it's more correct this way.

This way, we have four periods instead of the default of two.  With
only two periods, we don't get woken up often enough, and we
frequently encounter buffer overruns.  With four periods, we have more
time to breathe, and the buffer overruns magically disappear.

This setting is mostly useless for capture devices.  There's no point
in configuring it.

This is necessary because we'll never get woken up again by
epoll_wait() after a buffer overrun recovery, unless we start the PCM
explicitly before returning to the I/O loop.

Copy yet more code from the ALSA output plugin.

Copy some good code from the ALSA output plugin.

Fixes assertion failure in implicit destructor.

Call SeekDone() to avoid the freeze bug.