[with patch, positive review] follow-up to #6749: fix warnings when building reference manual

[mvngu]

As the subject says. This is a follow-up to ticket #6749.

[jhpalmieri]

I give it a positive review, too, but if you want to change the lines

    - ``seq`` -- Two different possible types: 
      - A sequence of pairs (weight, value). 
      - A sequence of reals (a value of 1 is assumed). 

by adding a blank line after the first one, it looks a little better (to me) when typeset. I'll give that a positive review in advance, so if you want to make the change, no need for more review.

[mvngu]

based on Sage 4.1.2.alpha4

[mvngu]

Replying to jhpalmieri:

I give it a positive review, too, but if you want to change the lines

    - ``seq`` -- Two different possible types: 
      - A sequence of pairs (weight, value). 
      - A sequence of reals (a value of 1 is assumed). 

by adding a blank line after the first one, it looks a little better (to me) when typeset.

Done.