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

Eliminate duplicate code.

Allow compiling test programs with only selected plugins.

This is nearly 4 times faster than the "portable" algorithm.

Refactor the conversion functions to classes and pass an instance to
the new function AllocateConvert().

Add class Context which wraps the Android/Java Context class and add a
JNI wrapper for method Context.getCacheDir().

The SDK for level 9 cannot be downloaded anymore.

A SimpleDatabase instance can now "mount" other Database instances at
certain locations.  This is used to use a new SimpleDatabase instance
for each storage mount (issued with the "mount" protocol command).
Each such instance has its own database file, stored in the directory
that is specified with the "cache_directory" option.

Finally, MPD runs on Android.  For some small value of "runs".  Very
much work left, too much to describe.

Doesn't work yet, just to get the Android port started.

Fixes build failure caused by commit d9466cad.

Prepare for providing everything in a shared library, to be embedded
in another process.

Use a listener interface instead of GlobalEvents.

Build was broken by previous commit.