The string "base" is understood by locate_parse_type(), but not by
listAllUniqueTags().  The special tag type LOCATE_TAG_BASE_TYPE causes
a crash in PrintUniqueTag().

Fixes crash bug because mpd_connection_get_async() was called without
a connection.

Move code from CreateConfiguredDatabase() and add XDG support.  This
implements an automatic Linux fallback for the setting "db_file" if
none was specified.

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

Quick hack to allow using the database without GLib (for Android).

Lists files and directories.  Supports storage plugins.

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.

The problem with std::queue is that it doesn't give us enough control.
The method Clear() is a kludge already, but soon, we'll need
filtering.

Move to SimpleDatabase::GetSong() to give that method more control.

Code can now be reused in LookupSong().

Helps avoid unnecessary archive scans during database update on a
fresh MPD process.

This is what we get from the storage plugin via FileInfo.  Fixes a
compiler warning on Mac OS X where dev_t appears to be signed.