Fixed noop try statements in db tests
Execute safe queries by default.

The mongodb library was throwing large warnings that "The default of false will change to true in the near future" and that "This message will disappear when the default safe is set on the driver Db".
Add opsCollectionPerDoc option to Mongo storage.

If this is true, each document will have its own collection for its operations. If false, operations are put in a single large operations table keyed by docname. The former is faster and requires less storage, but does not easily scale beyond 12,000 or so documents (the maximum number of collections per database) and does not seem compatible with Mongo's sharding.
Merge branch 'master' into mongodb-single-ops-collection
Merge pull request #147 from bfirsh/mongodb-single-ops-collection

Add option to store ops in single MongoDB collection