png mime type is setup by rails 3.2 now
png mime type is setup by rails 3.2 now

it also happens to be setup by prawn, but at least in that case
there is no warning message about the PNG constant
concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse