Add support for libpng (PNG images)

Packages describing “png” as local USE flag

Package “png” Flag Description
sci-electronics/pcb PNG graphics export
app-misc/lcdproc Enable support for media-libs/libpng in the glcd driver.
media-libs/imlib2 PNG image loader support
app-text/mathtex Generate png images by default instead of gif
dev-ruby/barby Add support for writing PNG images using dev-ruby/chunky_png.
app-emulation/qemu Enable png image support for the VNC console server

All packages providing a “png” USE flag (122)