I had the same issue but I finally solved with the use off the (expensive) MiniDisplayPort to Dual-Link DVI adapter (MB571Z/A). But It had some extra attention. First there was nothing, no signal. When I also used the USB connetction suddenly the Dell did show up as an extended monitor at 1920 x 1080. But in the MAc OSX prefferences you could also set it to "Best fot this screen". And than then the "mirracle happend". Full native support! Very nice.
And it works also in combination with my Aten Cubiq DVI KVMP switch (CS1782A) to switch between my Macbook Air and a Windows 7 PC.
Thank you! and for the tip about the preferences.
Did your cable support audio? Also, I discovered that there is a DisplayPort Standard group website; the FAQs on this site <displayport.org> seem to me to say that DisplayPort 1.2 should support a monitor like the U2713HM AND that a cable that supports DiplayPort 1.1a will also fully support DisplayPort 1.2 which is the connection that the Dell has. So perhaps the most cost-effective method is to start with a MiniDP to DP cable and if that doesn't work then splash out on the MiniDP to DualLink DVI.