Must return -1 on error, not 0.  0 is root.

The previous commit was broken.  D'oh!

The IsActive() method returned true even if the timer was not active,
after it completed once.  This broke the state file timer, and the
state file was not saved periodically.

This was broken by commit 84d20d9e, which deleted the "!" from the
check.

This was broken by commit 84d20d9e, which deleted the "!" from the
check.

Turns out the lock-free code using atomics was not thread-safe.  The
given callback could be invoked by GLib before the source_id attribute
was assigned.  This commit changes the DeferredMonitor class to use a
Mutex to block the event loop until source_id is assigned.  This bug
does not exist in the 0.19 branch because it does not use the GLib
main loop anymore.

Make sure glibc gives us all features.

Fixes hanging child process in the "pipe" output plugin.

Kludge for libavahi-client quirk.

Add the debug-only flag "virgin" which gets checked by assert()
calls.  Fixes assertion failures when using zeroconf/avahi.

Users now have to call Close() explicitly.  This simplifies using the
class, as most users have automatic socket management already, and
Steal() had to be used often.

Debug-mode workaround for bogus assertion failure.

Add a flag that indicates whether the EventLoop is currently "busy".
As long as that flag is set, it does not need to be woken up - we can
simply add the DeferredMonitor to the list, and it will be caught by
EventLoop very soon.  This eliminates nearly all of the
DeferredMonitor overhead when compared to IdleMonitor, rendering
IdleMonitor mostly obsolete.

Reduce DeferredMonitor overhead.

Improved support for added events.

For std::find_if().

Move code from AlsaMixerPlugin.