Add trace macros into the event groups implementation.

Add trace macros into the event groups implementation.
Add a task pre-delete hook to allow the insertion of any port specific clean up when a task is deleted.
Increase use of 'const' qualifiers.
Add vPortCloseRunningThread() into the Win32 port layer to attempt to allow Windows threads to be closed more gracefully when a task deletes itself.

git-svn-id: https://svn.code.sf.net/p/freertos/code/trunk@2128 1d2547de-c912-0410-9cb9-b8ca96c0e9e2