[patch, rfc, 6?] Enable identical frame sanity check

[Andrew Cagney]

>> The other choice is to treat it as undefined and accept the warning.
> 
> 
> Both make sense to me.  Probably the warning is better.  I think we
> should figure out why inside_entry_func isn't stopping the backtrace
> before this even becomes an issue, though...

See my other post, inside_main_func() is broken when there are only 
minimal symbols.

BTW, the inside_entry_func test is disabled pending evidence supporting 
its need.  With inside_main_func fixed, there's still no evidence.

Andrew