Do some work on the btraceback on Solaris, we test to see what debugger is available...

Do some work on the btraceback on Solaris, we test to see what debugger is available and we prefer the debuggers in this order: dbx, gdb, mdb. Also enchanced the dbx bactrace somewhat that it always dumps all available threads (e.g. we also changed from lwp to threads for dbx). We also print some variables that the gdb script also dumps on a bactrace. Hopefully we get some better dumps using this. The mdb is used as a last resort as it should be always installed on a Solaris box (dbx and gdb may not) but at the moment I'm still trying to find out how to get some more understandable dumps from mdb as its rather rudimentary and more a crash debugger then a source code debugger.