Fixes for bugs that were causing lost timer interrupts and missing thread context switching

Hi myang,

I found two more bugs in the firmware. Both are related to the RTOS timer. The first one caused an occasional stop of thread switching. Intention in the code was to cause a manual TA0 interrupt, by setting CCIFG. But the code was not using the timer control register, but the compare value register. 

The other one was causing missing TA0 interrupts in cause a user timer is used in addition to the RTOS tick timer. I use such a user timer for porting an open source bluetooth stack. 

Bye

Matthias