Fixes hanging NFS client.

The standard has been renamed since the early draft that was
implemented in MPD.

The "current" attribute is a "song order", not a "song position".
This is usually the same - except in random mode.  Fixes Mantis ticket
0004073.

Fix incorrect description of the "songs" field and add missing
"albums" field.
Signed-off-by: Joachim Fasting <joachifm@fastmail.fm>

Simply return an empty WritableBuffer, not a nulled one.

Finally allows loading playlist files on a storage plugin.  Commit
297e2747 attempted to implement this, but failed due to this bug.

Necessary for "final" on gcc 4.6.

Use milliseconds precision to reduce rounding errors.

Use milliseconds precision to reduce rounding errors.

The unit of gme_info_t::length is milliseconds, not centiseconds.