Use ptrace options to follow children.

This is a possible fix to Parrot missing events for multi-threaded processes.
wait for child to start
Use EXITKILL ptrace option to ensure cleanup.

This is just an extra measure on top of what we already do using the watchdog
and signal handling.

Fixes #28.
Only modify fork/clone if necessary.
Continue the tracee after attaching.
Merge master.

Conflicts:
	parrot/src/pfs_main.cc
Use ptrace options for tracing children.

Fixes #60, #28.

* ccl/pull/472/head:
  Continue the tracee after attaching.
  Only modify fork/clone if necessary.
  Use EXITKILL ptrace option to ensure cleanup.
  wait for child to start
  Use ptrace options to follow children.