RFR (S) 7178741: SA: jstack -m produce UnalignedAddressException in output (Linux)

[Kevin Walls]

Hi,

I'd like to get reviews on this small SA fix:

http://cr.openjdk.java.net/~kevinw/7178741/webrev_8.00/

jstack -m follows native frames, and gets confused if it can't follow 
from frame pointer to saved frame pointer.  Additional sanity checks on 
the register values avoid lengthy exception messages in the middle of 
jstack -m output.

This kind of check has been in JDK6 for a while, so we want to get 
latest hs25 providing the same readable output.

There's another bug 6313816 for the same problem on Windows, but the 
change isn't the same there so I'm leaving the bugs separate.

Thanks
Kevin