Export the cached task comms to userspace. This allows user apps to translate
the pids from a trace into their respective task command lines.

[ Impact: let userspace apps reading binary buffer know comm's of pids ]
Signed-off-by: NAvadh Patel <avadh4all@gmail.com>
[ added error checking and use of buf pointer to index file_buf ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>