added checks for uncert. values and more verbose error msgs
added checks for uncert. values and more verbose error msgs


Former-commit-id: 54f3883a327bd91399c1db91b862169d079a1b17 [formerly d17fe0dd12d8dd5715066226d54ac9431f986da9]
Former-commit-id: d67cce1e82ff642baaadf69261cafc3132273295
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine