[MacPorts] #23125: graphics/libpng update version, tweak livecheck

[MacPorts]

#23125: graphics/libpng update version, tweak livecheck
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 Reporter:  rmsfisher@…             |       Owner:  ryandesign@…           
     Type:  update                  |      Status:  assigned               
 Priority:  Normal                  |   Milestone:                         
Component:  ports                   |     Version:                         
 Keywords:                          |        Port:  libpng                 
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Comment(by ryandesign@…):

 The [attachment:libpng-1.4.0.diff update to libpng 1.4.0] is
 straightforward enough, but yes, the library name is now libpng14.dylib
 and all the ports link with libpng12.dylib so they'll need a revbump right
 after.

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Ticket URL: <http://trac.macports.org/ticket/23125#comment:4>
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