loongson/pypi: links for xtraceback

loongson/mirror xtraceback-0.4.0-rc1.tar.gz
loongson/mirror xtraceback-0.3.3.tar.gz
loongson/mirror xtraceback-0.3.2.tar.gz
loongson/mirror xtraceback-0.3.1.tar.gz
loongson/mirror xtraceback-0.3.tar.gz
loongson/mirror xtraceback-0.2.tar.gz