libpng-1.6.5 has been released, to remove two stray lines in arm/arm_init.c that caused libpng to fail to compile when ARM support is enabled.  This problem was apparently due to a cut-and-paste error of some sort on my part.

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It's unfortunate that no one attempted to build libpng-1.6.4beta01 or rc01 on an ARM platform and reported the problem.  I don't have access to an ARM development platform myself, so I have to depend on others to test on one.