[O] ox-latex doesn't handle doi: links right

[Vladimir Alexiev]

A link like doi:10.1109/ICMEW.2015.7169818 is resolved in org to 
http://dx.doi.org/10.1109/ICMEW.2015.7169818.
(I mean that if I click to the link, I go to that URL)

However, ox-latex makes merely this:
   \url{10.1109/ICMEW.2015.7169818} 
which Acrobat tries to resolve as a local file.
Instead, ox-latex should make this:
   \href{http://dx.doi.org/10.1109/ICMEW.2015.7169818}
{doi:10.1109/ICMEW.2015.7169818}