+ Add configASSERT() into ARM Cortex-M ports to check the number of priority
bit settings.
+ Clear the 'control' register before starting ARM Cortex-M4F ports in case
the FPU is used before the scheduler is started. This just saves a few
bytes on the main stack as it prevents space being left for a later save
of FPU registers.
+ Added xSemaphoreGetMutexHolderFromISR().
+ Corrected use of portNVIC_PENDSVSET to portNVIC_PENDSVSET_BIT in MPU ports.
- Clear the SysTick current value register before starting the SysTick (only required if something uses SysTick before starting the scheduler).
- Ensure atomic operations are thread safe by executing clrex in the context switch.
