winex11.drv: Link the windows PNG format to the X image/png format.

dlls/winex11.drv/clipboard.c

@@ -293,6 +293,7 @@ static WINE_CLIPFORMAT ClipFormats[]  =
 /* Maps X properties to Windows formats */
 static const WCHAR wszRichTextFormat[] = {'R','i','c','h',' ','T','e','x','t',' ','F','o','r','m','a','t',0};
 static const WCHAR wszGIF[] = {'G','I','F',0};
+static const WCHAR wszPNG[] = {'P','N','G',0};
 static const WCHAR wszHTMLFormat[] = {'H','T','M','L',' ','F','o','r','m','a','t',0};
 static const struct
 {
@@ -303,6 +304,7 @@ static const struct
     { wszRichTextFormat, XATOM_text_rtf },
     { wszRichTextFormat, XATOM_text_richtext },
     { wszGIF, XATOM_image_gif },
+    { wszPNG, XATOM_image_png },
     { wszHTMLFormat, XATOM_text_html },
 };
 

dlls/winex11.drv/x11drv.h

@@ -635,6 +635,7 @@ enum x11drv_atoms
     XATOM_XdndTypeList,
     XATOM_WCF_DIB,
     XATOM_image_gif,
+    XATOM_image_png,
     XATOM_text_html,
     XATOM_text_plain,
     XATOM_text_rtf,

dlls/winex11.drv/x11drv_main.c

@@ -172,6 +172,7 @@ static const char * const atom_names[NB_XATOMS - FIRST_XATOM] =
     "XdndTypeList",
     "WCF_DIB",
     "image/gif",
+    "image/png",
     "text/html",
     "text/plain",
     "text/rtf",