ssa_signal_handler.c: Return an error if add2line can't find a function name

 run_add2line function skips garbage from add2line utility.
 For a skipped frame, it didn't print a line into backtrace, but
 returned success. As result, the frame disappeared from the trace.
ssa_signal_handler.c: Add frame number to back trace line

 In case of add2line utility failure, a frame number in
 backtrace line was absent.
ssa_signal_handler.c: Remove ssa_signal_handler before abort()

 abort will send SIGABRT. It may cause a race in ssa_signla_handler.
 In any case a application is going to exit. We don't need to handle
 SIGABRT sent from abort(), let to default signal handler
 to do its job.
configure: Check pstack utility in configure

 Some Linux distro include pstack utility instead of gstack.
 pstack and gstack have the same command line interface and
 are developed by the same author.
 See: http://linuxcommand.org/man_pages/pstack1.html
 http://linux.die.net/man/1/pstack