sigsegv protection (exp overflow)
don't return inf!
use errno=EOVERFLOW to signal an overflow (as my_strntod uses errno anyway)
if errno will be too slow, my_strtod can be changed to return overflow status in a parameter (like my_strntod does)


include/m_string.h:
  EOVERFLOW
mysql-test/r/insert.result:
  updated
mysql-test/r/mysqldump.result:
  updated
strings/strtod.c:
  sigsegv protection (exp overflow)
  don't return inf!
  use errno=EOVERFLOW to signal an overflow (as my_strntod uses errno anyway)
  if errno will be too slow, it my_strtod can be changed to return overflow status in a parameter (like my_strntod does)