Reprocess .png's as transparent (w/ GraphicsMagic since my local

copy of ImageMagic creates garbage transparent .png's).

PR: 30190
Backport: r570373


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@570377 13f79535-47bb-0310-9956-ffa450edef68