Footnotes in the float branch

[Luca Furini]

Hi all

I recently had the time (and the pleasure) to look at before-float 
implementation branch, and I played a bit with it.

I focused on the handling of footnotes, as I noticed that sometimes they 
were placed on a page following their citations without a real necessity 
to do it; as I wrote some time ago (and I rememeber there was some 
consesuns on this) this behaviour is acceptable for before floats, but is 
probably not what a user would expect for footnotes.

I have tried to fix this in the PageBreakingAlgorithm, computing a 
"minimum required index" for footnotes, so that no page break will be 
considered that unnecessarily defers some old footnotes to the next page.

I'm attaching a diff file showing the changes (or maybe should I just 
apply it?); after applying the patch, there are 4 more passing testcases 
(foonote_footnote-separator, footnote_large, footnote_positioning_{4,5}) 
and no regressions. Testcases footnote_positioning_{2,3} still generate 
some run-time exception, and in the next days I'm going to see what's 
wrong with them.

I add just a few comments about the new classes: I must admit that it took 
me a while to see and understand the interaction between the 
PageBreakingAlgorithm and the Footnotes / BeforeFloats Record, together 
with their inner Footnotes / BeforeFloats Progress.

In particular, at the beginning I thought the *Progress classes were just 
convenience classes to get "pieces" of footnotes and floats without 
directly fiddling with element lists, and I found only later that their 
methods can actually create new active nodes.

Another thing that I find a bit strange is that the PageBreakingAlgorithm 
does not directly interact with the before floats, as the calls to 
BeforeFloatsProgress.consider() are "hidden" in the FootnotesProgress 
class.

So, I was wondering whether it wouldn't be more "clear" to have the 
PageBreakingAlgorit control all the node creation logic, after having 
accessed information about footnotes and floats that could be placed in 
the page via the helper classes.

WDYT?

Regards
    Luca