RFR: Track interior location when verifying matrix

[Roman Kennke]

I ran into a crash because the verifier did not track the interior loc
when verifying matrix.

I added code to avoid the crash (i.e. check _interior_loc == NULL), and
also added code to actually track the interior location when verifying
matrix.

http://cr.openjdk.java.net/~rkennke/verifier/webrev.00/
<http://cr.openjdk.java.net/%7Erkennke/verifier/webrev.00/>

Ok?

Roman