Patch: Remove exception catching from normal path in Arrays.equals.

[Andrew Haley]

Mohan Embar writes:
 > Hi Andrew,
 > 
 > > > Let me know if you want me to submit a patch. Otherwise, I'll walk
 > > > away from this.
 > >
 > >Sure, go ahead.  I'm a bit nervous about the throw new RuntimeError
 > >part because some broken libgcj targets still don't have working
 > >backtrace.  Perhaps it needs to be conditional on HAVE_BACKTRACE.
 > 
 > I'll submit a patch for this. I thought about the conditional HAVE_BACKTRACE
 > too. The crux of the question is: on failure, should the helper method do
 > some sort of exception throwing or return a null value? You said previously
 > that you didn't like the null checking....

If HAVE_BACKTRACE is not set, do not scan the stack but return null.

If HAVE_BACKTRACE is set, we believe that backtrace() works.  So,
throw an exception if we don't find a caller.

I await the firestorm...

Andrew.