don't call escape_string_for_mysql() unnecesary
  don't overwrite local buffer
escape_string_for_mysql():
  take a length of the destination buffer as an argument


include/my_sys.h:
  prototype changed
libmysql/libmysql.c:
  prototype changed
mysys/charset.c:
  escape_string_for_mysql():
    take a length of the destination buffer as an argument
sql/field.cc:
  Field::quote_data():
    don't call escape_string_for_mysql() unnecesary
    don't overwrite local buffer
sql/item.cc:
  prototype changed
sql/sql_prepare.cc:
  prototype changed