This reduces duplicates in the music database by hiding the original
song file when it is referenced by a CUE sheet.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1275

This reverts commit 9200fa6d.  It was
wrong because it works only if the target song has already been
scanned.

make_pair is an old C++98 function that can be replaced by modern
shorter constructs.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1019

Prepending "../" to absolute URIs would break them.

When updating everything, this did work, but if updating only a
subdirectory, the ".mpdignore" in the parents were not used.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1172

Shorter.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Preparing for a variant of TimerEvent with coarse 1-second
granularity, but cheaper (with a timer wheel).

No need to copy it to a buffer.

This allows users to disable the "CUE files as directories" feature
without having to disable the CUE playlist plugin completely.  This
feature has been annoying some users.

Shorter.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Similar to commits 1686f4e8 and
30a5dd26

"DEFAULT" is a bad name - all it says is that it's the default value,
but it doesn't say what it means.  The name NOTICE mimics the syslog
level.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/846