Add a start hook that can be setup to call a function in the context of a new...

Add a start hook that can be setup to call a function in the context of a new thread before the new threads main() has been called.

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5571 42af7a65-404d-4744-a932-0658087f49c3