Changes made to pristine png source by mozilla.org developers.
2004/10/07 -- Synced with libpng-1.2.7 tree
2004/10/07 -- add mozpngconf.h (bug 208607)
2006/09/22 -- fix security problem with too-small error message buffer
2006/09/22 -- fix security problem with too-small gamma-shift array.