[MacPorts] #28385: libpng: update to 1.5.x

[MacPorts]

#28385: libpng: update to 1.5.x
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 Reporter:  rmstonecipher@…             |       Owner:  rmstonecipher@…           
     Type:  update                      |      Status:  new                       
 Priority:  Normal                      |   Milestone:                            
Component:  ports                       |     Version:                            
 Keywords:  haspatch                    |        Port:  libpng                    
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Comment(by ryandesign@…):

 Right. Without that, users might download a binary, only to have rev-
 upgrade find out that it's broken because it links with the wrong library
 version, and then have to rebuild it on the user's system anyway. rev-
 upgrade is there to help us figure out which ports need a revision
 increase, not to eliminate that need.

 Also, users could turn rev-upgrade off. I certainly do; even the small
 amount of time it takes on my current Mac adds up, given how much I use
 MacPorts on an average day.

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Ticket URL: <https://trac.macports.org/ticket/28385#comment:16>
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