New stack trace code

[Bryce McKinlay]

Andrew Haley wrote:

>Now that we have full line number info for shared libraries, it seems
>that calls to addr2line are taking far too much time in any
>application that does much logging.  
>
>We need a way to disable line number info, even when we have our own
>built-in dwarf reader.
>
>Something like this, perhaps.
>
Try -Dgnu.gcj.runtime.NameFinder.use_addr2line=false

addr2line is certainly too slow when an application calls it frequently, 
but I think maybe we should wait until we do some performance tests on 
the dwarf2 reader before deciding whether it is neccessary for an option 
that disables line numbers globally. Also, the overhead of getting line 
numbers for interpreted frames is small, so I don't think it makes sense 
to disable for that case as well.

Bryce