astobj2.c/refcounter.py: Fix to deal with invalid object refs.

* Make astob2 REF_DEBUG output an invalid object line when an invalid ao2
object ref/unref is attempted.  This is similar to the
constructor/destructor lines.

* Fixed refcounter.py to handle skewed objects that have
constructor/destructor states.

* Made refcounter.py highlight the invalid ao2 object refs by putting them
in their own section of the processed output file.

* Made refcounter.py highlight unreffing an object by more than one that
results in a negative ref count and the object being destroyed.  The
abnormally destroyed object is reported in the invalid and finalized
object sections of the output.

Review: https://reviewboard.asterisk.org/r/3971/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@423349 f38db490-d61c-443f-a65b-d21fe96a405b