Name the generated HPKG files properly

* rule AddPackageFilesToHaikuImage: Add "flags" parameter. The only
  supported flag is "nameFromMetaInfo". It causes the packages to be
  copied under their canonical file name onto the image.
* Use the new flag for all generated packages save haiku_loader.hpkg.

build/scripts/build_haiku_image

@@ -219,6 +219,12 @@ downloadFile()
 }
 
 
+packageFileName()
+{
+	$package info -f "%fileName%" "$1"
+}
+
+
 mkdir -p $tmpDir
 copyrightsFile=$tmpDir/copyrights
 $rmAttrs -f $copyrightsFile