[libpng15] Removed scripts/makefile.elf which has not worked since libpng-1.4.x
[libpng15] Imported from libpng-1.5.19beta04.tar
[libpng15] Bump version to 1.5.19beta05
[libpng15] Eliminated use of "$<" when copying $PNGLIBCONF_H_PREBUILT

in makefiles. This does not work on some versions of make; bug introduced
in libpng version 1.5.19beta03.
[libpng15] Imported from libpng-1.5.19beta05.tar
[libpng15] Bump version to 1.5.19beta06