[tex-k] TeXbook: space -> control space

[Igor Liferenko]

>     other common abbreviations like `Fig.'\ and `cf.'\ and `vs.'\ and `resp.';

Sorry, this is not a good example, because a quote is used after the dot.
This line from texbook.tex is a better example:

    but not before `|---|'; cf.\ Appendix~H\null. The ^|\relax| at the end of