Commit d42c0f1d added an OS X-specific
method of calling mpd_main_after_fork(), which uses Grand Central
Dispatch. Since this uses a block literal, it breaks compilation on
compilers which don't support the block extension, e.g. non-Apple
compilers. This affects users on older OS X releases with GCD (which
depend on older Clang releases, or Apple GCCs, which don't support the
C++11 features MPD needs); or which don't support GCD at all (10.5 and
lower).

This patch changes the #ifdef so that the non-GCD code is used
as it was on OS X before this patch if blocks aren't available, via
checking __BLOCKS__ macro.

This reverts commit f0be48ff
(except for the NEWS entry).

If libdispatch (GCD) is used before forking, it
can't safely be used again after forking.

Break the mainloop and terminate run call.

Don't fail to start if mpd.conf does not exist; just use default
values.

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

Hard-coded path.  Will be replaced soon.

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.

Fixes nullptr dereference (regression by commit df5f9f4a).

Ignore the storage configuration if FLAG_REQUIRE_STORAGE is not set in
the DatabasePlugin.

The new method IsPlugin() replaces the "is_simple" flag.

Use a listener interface instead of GlobalEvents.

Fix build failure.

Fixes nullptr dereference.