RR(S): 8008807: SA: jstack crash when target has mismatched bitness (Linux)

[Kevin Walls]

Hi,
This is a crash I stumbled upon: jstack -m will crash when it doesn't 
match the bitness of its target.  On Solaris we check and give an 
exception message, Linux should do similarly.

http://cr.openjdk.java.net/~kevinw/8008807/webrev.00/

Here I've gone with checking and denying the attach attempt as early as 
possible.

Thanks
Kevin