Then don't write invalid HTML.

<a href="http://www.nationmaster.com/encyclopedia/Formulation-of-Maxwe
+ll's-equations-in-special-relativity">this link</a>
[download]

produces this link.

[http://www.nationmaster.com/encyclopedia/Formulation-of-Maxwell's-equ
+ations-in-special-relativity|that link]
[download]

produces that link.

Unmatched quotes in HTML attributes are currently rejected as too troublesome to try to DWYM.

Note that either URL-escaping or HTML-escaping works in HTML links (as per the standard) so <a href="http://www.google.com/search?q=&quot;vu do%22">"vu do"</a> produces "vu do". Neither type of escaping currently work in [http://...] links but that is likely to change eventually (update: oh, URL escaping works in this case but not in other link types; HTML escaping doesn't work).