When there are many watched files, keeping track of them using lists
is suboptimal. Using sets improves the performance considerably.
(Bitbake rev: 1e96df260e47d160dbd36bfc92c31ef06266f662)
Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>