When navigating using C-n/C-p with a high key repeat rate, causing
linum-schedule to be called many times in quick succession,
linum-update-current gets called as many times in linum-schedule,
eventhough one call per round should be enough to renumber the lines.

This patch adds a linum-delay-seconds option defaulting to 10ms to delay
the call to linum-update-current, thus coalescing all calls to
linum-update-current until Emacs settles for 10ms.

--
Kind regards,
Loong Jin