- backport patch from 5.0
 - "table" can be NULL in temporary fields used for type conversion


sql/field.cc:
  table can be NULL in temporary fields used for type conversion.
  Store value in field as if db_low_byte_first was set.
sql/field.h:
  table can be NULL in temporary fields used for type conversion.
  Store value in field as if db_low_byte_first was set.