updated mean loss map computation
updated mean loss map computation


Former-commit-id: 5abcd824ecf1f9deb8c6247a81b43171d99aa594 [formerly 01d9a22018172fc63d7633fb20b3c3605b07d8bf]
Former-commit-id: 3003d7b864036ba3dcf17c831a9a7c86000b9b5e
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine