Resubmit of spy_file chisel.  See github sysdig issue #230 for previous conversation.

Example usage:

[root@web01 ~]# sysdig -c spy_file "rw /var/log/messages"
22:10:30.827285182 rs:main(25251) W 72B /var/log/messages
Aug 22 22:10:30 web01 mod_wsgi[23998]: XXXXXXXXXX RPC: get_map(raw = 1)

22:10:31.179507012 rs:main(25251) W 72B /var/log/messages
Aug 22 22:10:31 web01 mod_wsgi[26529]: XXXXXXXXXX RPC: get_map(raw = 1)
cleanups
improve the heuristic to detect when an entry in /proc is a kernel thread.
wrong file name