Fix whitespace in coercion_and_categories.rst

[jdemeyer]

devel/sage/doc/en/thematic_tutorials/coercion_and_categories.rst mixes TABs and spaces for indentation, which is very bad style and might also lead to doctesting trouble.

Depends on #11490

CC: @simon-king-jena

Component: documentation

Author: Jeroen Demeyer

Reviewer: Simon King

Merged: sage-5.8.beta2

Issue created by migration from https://trac.sagemath.org/ticket/14182

[simon-king-jena]

comment:1

How to replace tabs by four blank spaces (in linux or vim)? Perhaps you can answer faster than I can look up in google...

[jdemeyer]

Attachment: 14182_whitespace.patch.gz

[jdemeyer]

Author: Jeroen Demeyer

[simon-king-jena]

comment:3

OK, you were faster. I found sed 's/\\t/ /g' oldcode.py >newcode.py in google...

[simon-king-jena]

comment:4

Good. After applying the patch, I could not find any tab space in the code. Since the patch does not change the actual text, since the documentation built w/o trouble, and since the result looks fine in the browser, I give it a positive review.

[simon-king-jena]

Reviewer: Simon King

[roed314]

Dependencies: #11490