Add in constants which let you explicitly check if endian conversion would do anythin...

Add in constants which let you explicitly check if endian conversion would do anything. This was needed for a case where a piece of data was within a larger data type. When the larger data type was swapped, the location of the smaller data type would move.

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extra : convert_revision : 4c904c964678529c72b8f1044dfcb400604f6654