SIGABRT is sent to relevant processes after a timeout


client/mysqltest.cc:
  Fixed signal handlers to mysqltest actually dumps core
mysql-test/lib/My/CoreDump.pm:
  Added support for dbx
mysql-test/lib/My/SafeProcess.pm:
  Added dump_core to force process to dump core
mysql-test/lib/My/SafeProcess/safe_process.cc:
  Traps SIGABRT and sends this on to child
mysql-test/mysql-test-run.pl:
  When test times out, force core dumps on mysqltest and servers