- Replace per-thread signal()'s with SetUnhandledExceptionFilter().
The only remaining signal() is for SIGABRT (default abort()
handler in VS2005 is broken, i.e removes user exception filter)
- remove MessageBox()'es from error handling code
- Windows port for print_stacktrace() and write_core()
- Cleanup, removed some unused functions
Define a new CPP symbol that the target OS is Linux, and use it where only the OS matters and not the threads Library.
Until now, 'HAVE_LINUXTHREADS' was used to indicate "Target is Linux" in many places.
When we support configuration with NPTL but no Linuxthreads, this misuse must cease.
