The purpose of this is to support library backends making their own
calculation of these id's, which is relevant if they have more information
available than just album_artist and album.
This also removes a bunch of sqlite extension code plus some triggers, which
in itself is probably an improvement.
If a file gets updated/rescanned we generally don't want to reset the above
values. This commit adds DB_FLAG_NO_ZERO, which marks a field so that
db_file_update() will only update it if the new value is non-zero (i.e. the
caller probably has a "better" value).
Properly handle the tail of the data buffer, accessing the tail as an
unsigned char array instead of a uint32_t array.
Issue spotted by Peter Carmichael.
Move the custom collation and daap_songalbumid() function to a custom SQLite
extension. This will make it possible to use them both from any SQLite client
or frontend.
