Make package-header caption backward-compatible

The current html generator of this branch wraps the package-header
caption as a div, which does not work (without style adjustments) with
the old themes. Changing it from div to span does the trick, without
needing to adjust the old stylesheets.

haddock-api/src/Haddock/Backends/Xhtml/Layout.hs

@@ -74,8 +74,8 @@ sectionName = paragraph ! [theclass "caption"]
 -- If it would have otherwise been empty, then give it the class ".empty".
 nonEmptySectionName :: Html -> Html
 nonEmptySectionName c
-  | isNoHtml c = thediv ! [theclass "caption empty"] $ spaceHtml
-  | otherwise  = thediv ! [theclass "caption"]       $ c
+  | isNoHtml c = thespan ! [theclass "caption empty"] $ spaceHtml
+  | otherwise  = thespan ! [theclass "caption"]       $ c
 
 
 divPackageHeader, divContent, divModuleHeader, divFooter,