Clear up a few compiler warnings.

Clear up a few compiler warnings.
Correct header comments in the UARTCommandConsole.c file used in the SmartFusion2 demo.
Exercise the new xQueueSpacesAvailable() function in the MSVC demo.
Add defaults for the new traceMALLOC and traceFREE trace macros.
Catch tasks trying to exit their functions in the Cortex-M0 ports.
Add additional comments to timers.c in response to a support forum question.
Initialise _impure_ptr prior to the first task being started.
Prior to V7.5.0 a yield pended in the tick hook would have occurred during the same tick interrupt.  Return pdTRUE from xTaskIncrementTick() if a yield is pending to revert to that behaviour.

git-svn-id: https://svn.code.sf.net/p/freertos/code/trunk@2051 1d2547de-c912-0410-9cb9-b8ca96c0e9e2