Fix to check library in use during runtime.
Fix for Bug#16995, "idle connections not being killed due to timeout when NPTL is used".


BUILD/SETUP.sh:
  To avoid warnings during compilation.
configure.in:
  Fixed configure so that it can correctly detect
  between NPTL and Linuxthreads.
include/my_global.h:
  Fix for Linuxthreads.
include/my_pthread.h:
  Added defines for different libraries that can be detected.
  Currently only 'other', 'nptl', and 'lt' (linuxthreads) are
  being used.
  
  changed sigset() and signal() to my_sigset() and my_signal()
include/thr_alarm.h:
  Removed defines for Linuxthreads. This is now detected during
  runtime and handled in the thr_alarm.c
mysys/my_pthread.c:
  Runtime check for library.
mysys/thr_alarm.c:
  Runtime checks for library and corresponding
  signals.
sql/mysqld.cc:
  Added function for detecting thread library in use
  during start-up.
  
  THR_KILL_SIGNAL removed, setting signals during runtime.