iteration 1 for enabling compat with jstests/core:array*.js, array_*.js, arrayfind*.js . Added explain and hint. Also added getSiblingDB, Array and Object additional methods.
iteration 2: added getMongo() shell helpers, copyDatabase, dropDatabase, hashing mechanism; got most of core/a*.js to pass
iteration 3:
1. Added assertion methods.
2. Added support for ObjectId.
3. Added support for bulk operations. Todo: add BulkWriteError support.
4. Added other cursor methods like size, arrayAccess, countReturn. Todo: access indexing facility.
5. Added support for hinting and batchSize.
6. Added support for getMongo.
7. Added other DBMethods like getIndexKeys.
8. Added collection methods like createCollection, hostInfo, currentOp, and others.
Merge pull request #19 from alabid/db/core-tests

iteration 1 for enabling compat with jstests/core:array*.js, array_*.js,...