Correct duplicate EXIF and TIFF tags

**EXIF**

`RelatedImageWidth` should be 0x1001.
`RelatedImageLength` should be 0x1002.

http://www.exiv2.org/tags.html


**TIFF**

There was a typo in the spec, `BestQualityScale` should be 50780. 

http://www.asmail.be/msg0055321032.html 

Here's a corrected spec PDF, version 1.4.0.0 from June 2012:

https://a248.e.akamai.net/f/1953/8974/2h/wwwimages.adobe.com/content/dam/Adobe/en/products/photoshop/pdfs/dng_spec_1.4.0.0.pdf