NSH will now run files from the file system; Add logic to unload and clean-up...

NSH will now run files from the file system; Add logic to unload and clean-up after running a task from a file system; Extensions to builtin apps from Mike Smith

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5529 42af7a65-404d-4744-a932-0658087f49c3