command: for OSD, format cache property as integer

For convenience. Use ${=cache} to get the old formatting.
input.conf: change LEFT/RIGHT keys to seek 5s instead of 10s
input: fix event wakeup

When a new event was added, merely a flag was set, instead of actually
waking up the core (if needed). This was ok in ancient times when all
event sources were part of the select() loop. But now there are several
cases where other threads can add input, and then you actually need to
wakeup the core in order to make it read the events at all.
vdpau: allocate surfaces by age

Whether this helps is probably questionable and depends on the GPU. But
the vaapi code does it too.