implemented a new WebUI patch to force addon version download URLs to

carry a valid text/plain content-type no matter what the corresponding
addon URL returns. This fixes #480.

buildroot-external/patches/occu/0047-WebUI-ForceAddonVersionContentType.patch

@@ -0,0 +1,34 @@
+--- occu/WebUI/www/config/cp_software.cgi.orig
++++ occu/WebUI/www/config/cp_software.cgi
+@@ -452,18 +452,21 @@
+   puts "<script type=\"text/javascript\">translatePage('#messagebox')</script>"
+   global swVersion swUpdate
+   cgi_javascript {
++    puts "function getVersion(url, callback) {"
++    puts "  var xhr = new XMLHttpRequest();"
++    puts "  xhr.onreadystatechange = function () {"
++    puts "    if (xhr.readyState === 4 && xhr.status === 200) callback(xhr.responseText);"
++    puts "  };"
++    puts "  xhr.open(\"GET\", url, true);"
++    puts "  xhr.overrideMimeType(\"text/plain; charset=iso-8859-1\");"
++    puts "  xhr.send();"
++    puts "}"
+     for {set i 0} {$i <= $loop} {incr i} {
+       if { [info exists swUpdate($i)] } {
+-        puts "var anchor = document.getElementById(\"availableSWVersion_$i\");"
+-        puts "var iframe = document.createElement(\"iframe\");"
+-        puts "iframe.src = \"$swUpdate($i)?cmd=check_version&version=$swVersion($i)\";"
+-        puts "iframe.frameBorder=0;"
+-        puts "iframe.marginHeight=0;"
+-        puts "iframe.marginWidth=0;"
+-        puts "iframe.width=100;"
+-        puts "iframe.height=20;"
+-        puts "iframe.scrolling='no';"
+-        puts "anchor.appendChild(iframe);"
++        puts "getVersion(\"$swUpdate($i)?cmd=check_version&version=$swVersion($i)\", function(contents) {"
++        puts "  document.getElementById(\"availableSWVersion_$i\").innerHTML = contents;"
++        puts "});"
++        puts "document.getElementById(\"availableSWVersion_$i\").innerHTML = \"n/a\";"
+       }
+     }
+   }