rtimer-tests/: collect and merge coverage data for _rtimer
rtimer-tests/run: allow double quotes in sections

$s expanded the line before "eval" which exposed the double quotes.
\$s defers expansion until the assignment.
core/sys/rtimer.c (run_deferred): avoid set_queue race; avoid partial copy

This change fixes two issues:

1) we can only test whether set_queue contains any pending rtimers when
   "setting" is set,
2) we must copy the new rtimer setting before locking (the rtimer list)
   because these settings can be changed while locked.
core/sys/rtimer.c, rtimer.h: have two queues for rtimers waiting to be set

This way we can keep different levels of interrupts out of each other's
hair.
rtimer-tests/sim.c (reset_sim): update for rtimer.c changes

New variable and variables/fields becoming arrays.