Changed mime type for MNG from image/png to image/x-mng and JNG to image/x-jng

diff --git a/coders/png.c b/coders/png.c
index e45ab5e..8b55d25 100644
--- a/coders/png.c
+++ b/coders/png.c
@@ -7496,7 +7496,7 @@
   if (*version != '\0')
     entry->version=ConstantString(version);
 
-  entry->mime_type=ConstantString("image/png");
+  entry->mime_type=ConstantString("image/x-mng");
   entry->module=ConstantString("PNG");
   entry->note=ConstantString(MNGNote);
   (void) RegisterMagickInfo(entry);
@@ -7633,7 +7633,7 @@
   entry->magick=(IsImageFormatHandler *) IsJNG;
   entry->adjoin=MagickFalse;
   entry->description=ConstantString("JPEG Network Graphics");
-  entry->mime_type=ConstantString("image/png");
+  entry->mime_type=ConstantString("image/x-jng");
   entry->module=ConstantString("PNG");
   entry->note=ConstantString(JNGNote);
   (void) RegisterMagickInfo(entry);