[Review] Remove procfs dependency of truss

Following the suggestion in idea page, I proposed the attached patch.
I didn't change any kernel part because I think PTRACE(2) is
functional although man page didn't document it.

I tested the patch under i386 and amd64 box. The help on testing and
code review will be appreciated.

To test, please try the following commands:
1. truss ps
basic stuff
2. truss -o output ps
output the result to file
3. truss -f -o output sh -c "ps"
test follow fork
4. start TOP(1) in another session, the
truss -p <pid_of_top>

-- 
-Howard