Remove the data_time parameter from decoder_data().  This patch
eliminates the timestamp counting in most decoder plugins, because the
MPD core will do it automatically by default.

This patch prepares support for floating point samples (and probably
other formats).  It changes the meaning of the "bits" attribute from a
bit count to a symbolic value.

Let the audio_check library verify the audio format in all (relevant,
i.e. non-hardcoded) plugins.

Internally, use only the integer time.  When needed, convert it to a
floating point seconds value.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

When parsing the songlength database fails, the code forgot to free
the memory allocated by the raw file data.

The caller is responsible fro freeing GError objects.  That
g_error_free() call was missing in two places.

The error handler dereferences GError*, but did not retrieve that
object from g_file_get_contents().

[mk: added autoconf test; fixed songlen_data_size type]

It makes no difference right now, but we're about to add an endianness
flag and will want to make sure it's correctly initialised every time.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

[mk: fixed whitespace errors; use delete_song() instead of
songvec_delete()]