libpng15 + dev respin

[Riccardo Mottola]

Hi,

especially for Laurent: I was finally able to do a libpng-15 respin with 
its dev versioned dev package.
The dev-package is really minimal but I hope it is enough? IN case 
please add yourself or tell me which precise file to add, one by one, 
explicitely.

I uploaded it successully, perhaps they can be already installed on the 
buildfarm

I am still working on the 16 package: I get a strange error I didn't get 
in the unversioned one and it makes no sense since I did not change 
anything in the content of the packages when versioning. I am doing a 
total clean build on all platforms and it takes a lot of time.

Riccardo