Allow vfork system call.

This also moves creation of the child process data structures to the
PTRACE_EVENT_V?FORK handling.
Disable use of helper library by default.

Includes new --helper long option to enable it.
Allow vfork system call.

* ccl/pull/497/head:
  Disable use of helper library by default.
  Allow vfork system call.
Add parrot_package_create to ignore.
Sort by long-option.
Hardcode Linux 2.5.46 base version requirement.

Linux 2.5.46 was circa 2003.

The requirement was already enforced in tracer.c:80 via commit
5ef1eca8d78eea302c2fb82a9d755973cd6bd8ce. This commit just enforces that
consistently and removes unnecessary checks.