Fixes busy loop when USB sound device gets unplugged (Mantis bug
#3824).

Use LockSynchronousCommand() instead of SynchronousCommandLocked().
Fixes regression from commit ef663810 (dead lock due to cond_wait with
unlocked mutex).

This plugin has been defunct ever since Last.fm changed their
protocol.  Since there is no volunteer willing to fix the plugin, I'm
removing it now.

The MPD core will add this as a prefeix.

Implement Mantis ticket 0003646.

Reduce the TagItem overhead.

Reduce heap allocator overhead.

Add nullptr check, and return early from glue_db_init_and_load().

Since Debian package 1:0.8.8.4-4, the pkg-config file does not contain
-I/usr/include/libmodplug anymore, and we need to add the
"libmodplug/" prefix to the #include line.

When playing finite http streams, e.g. something from soundcloud,
eventloop stalls after pausing writefunc. TimeoutMonitor is cancelled
by the time resume happens, so when enough data is consumed writefunc
is called only once. Calling InvalidateSockets() from
input_curl_resume() seems to fix the issue.

Previously, the pointer was moved to undefined memory.