Added checking of return value from malloc() in reg_init()


client/mysqltest.c:
  Added comment
dbug/dbug.c:
  Removed not needed test
mysys/charset.c:
  Added checking of return value from my_once_alloc()
regex/reginit.c:
  Abort if out of memory in reg_init() (unlikely)
sql/item_strfunc.cc:
  Added comment