RIOT-OS/RIOT — pull request #1193 by LudwigOrtmann (2014-05-16 13:51:45+00:00)
Title: core/hwtimer: disable interrupts in hwtimer_remove

Before only the hardware timer's own interrupt was being disabled.
This led to a race condition in the following scenario:

```
Thread1:
hwtimer_remove()
hwtimer_arch_disable_interrupt();

// INTERRUPT -> Thread2 (which has a higher priority than Thread1) gets scheduled

Thread2:
...
hwtimer_remove()
hwtimer_arch_disable_interrupt(); // hwtimer interrupt is already disabled
...
hwtimer_arch_enable_interrupt();
...
// yield | terminate -> Thread1 gets scheduled again

Thread1:
... // these instructions are being run with the hwtimer interrupt enabled
hwtimer_arch_enable_interrupt(); // hwtimer interrupt is already enabled
```

Fixes #924