POSIX requires that a signal handler defined with sigaction()
is not reset on delivering a signal unless SA_NODEFER or
SA_RESETHAND is set. It is therefore unnecessary to redefine
the handler on signal delivery on platforms where sigaction()
is used without those flags.

include/my_alarm.h:
  Renamed DONT_REMEMBER_SIGNAL ->
  SIGNAL_HANDLER_RESET_ON_DELIVERY.
include/my_global.h:
  Renamed DONT_REMEMBER_SIGNAL ->
  SIGNAL_HANDLER_RESET_ON_DELIVERY. The latter is now defined
  only on non-BSD platforms missing the POSIX sigaction()
  function.
libmysql/libmysql.c:
  Renamed DONT_REMEMBER_SIGNAL ->
  SIGNAL_HANDLER_RESET_ON_DELIVERY
mysys/thr_alarm.c:
  Renamed DONT_REMEMBER_SIGNAL ->
  SIGNAL_HANDLER_RESET_ON_DELIVERY
sql/mysqld.cc:
  Renamed DONT_REMEMBER_SIGNAL ->
  SIGNAL_HANDLER_RESET_ON_DELIVERY