Move get_thread_lib to mysys/my_pthread.c
Set 'thr_client_alarm' to signal number used by thr_alarm to give alarms



include/my_global.h:
  Fixed to be same as in 5.1
include/my_pthread.h:
  Move things around to be more in line with rest of code
include/thr_alarm.h:
  extern of thr_client_alarm
mysys/default.c:
  Fixed two wrong pointer incrementations.
mysys/my_pthread.c:
  Cleanup: Use variable thr_client_alarm
mysys/my_thr_init.c:
  Detect thread library at startup
mysys/thr_alarm.c:
  Set thr_client_alarm depending on which thread library we are using
sql/mysqld.cc:
  Move get_thread_lib to mysys/my_pthread.c