openmpt: "author" metadata key got renamed to "artist" in libopenmpt

Signed-off-by: Joern Heusipp <osmanx@problemloesungsmaschine.de>
openmpt: Write "tracker" to GST_TAG_APPLICATION_NAME instead of GST_TAG_ENCODER

Signed-off-by: Joern Heusipp <osmanx@problemloesungsmaschine.de>
Fix package name in wscript --with-package-name

Signed-off-by: Joern Heusipp <osmanx@problemloesungsmaschine.de>