[Crash-utility] GCORE: add directly show backtrace function in crash

Hi Daisuke, I create a new option "-tT" for gcore, so that it could display bt for user space directly inside crash itself, without needing to dump a separated core file image, and analyze it in a different gdb env. The attached patch is directly based on below patch, and verify over ARM platform. http://osdir.com/ml/general/2012-10/msg32677.html Before use the corresponding gcore command, we need set env in crash by: crash>> gdb set solib-search-path [system lib path] crash>> gdb file [user space program symbol file] crash>> gcore -t [user space thread id] Thanks, Lei