xsidle+jslock: Lame hackaround to fix high CPU load

Suppose I manually lock my screen (i.e., run jslock). After some
minutes, xsidle will reach the specified time and tries to start jslock.
This, in turn, quits immediately because slock is already running.
Result: Endless fork-exit-fork-exit-fork-exit and high CPU load.

Proper way to fix this: When jslock detects that slock is already
running, it should wait for slock to exit.

Easy way to fix this: Just slow down the fork-exit-fork-exit...