pthread_setcanceltype() and pthread_testcancel() do not have to be system calls if cancellation points are not enabled.

Update TODO, cosmetic changes, spelling -- US English spells it canceled and canceling vs cancelled and cancelling.  No idea why.

pthread_mutex_destroy(): Fix an error in destorynig a mutex which can occur after a pthread has been canceled while holding the mutex.

cancellation points are basically function.  More tested is needed and additional cancellation points must be implemented before this can be merged back to master.

Merged in david_s5/nuttx-3/david_s5/typo-in-stm32f76xx77xx_pinmaph-edited-on-1481298811328 (pull request #182)

Typo in stm32f76xx77xx_pinmap.h edited online with Bitbucket

Added STM32F469 RAM size and deliberated STM32F446 size

Merged in david_s5/nuttx-2/david_s5/i-was-wrong-the-original-commit-was-cor-1481231650458 (pull request #179)

I was wrong - the original commit was correct. Assume a write op on the last word: address of 0xxxxxfe and count of 2. It is a valid operation and address+count is == STM32_FLASH_SIZE - so that is OK