[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 rmstonecipher@…):

 With permission I would like to apply the attached patch to the Portfile
 to upgrade the ported libpng to 1.4.5.[[br]]
 1.5.0 is available upstream, but the homepage warns against using it due
 to a bug that will be fixed in 1.5.1.[[br]]
 With an estimated release date of 2011-01-20, updating this port now
 should give us a few days to identify which ports need libpng 1.2.x and
 which can utilize libpng 1.![4,5].x.[[br]]
 May I give it a try?

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Ticket URL: <https://trac.macports.org/ticket/23125#comment:15>
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