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

Iteration 1
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Added the following:
1) NodeJS' built in assert module, with assert.eq as a shorthand for assert.equal. Might need to make it a shorthand for assert.deepEqual, not sure if assert.eq is a deep equality check or not.

2) Array.sum, Array.avg, Array.stdDev: https://github.com/mongodb/mongo/blob/master/jstests/core/array3.js

3) print() as a wrapper around console.log()

4) ShellIterator.itcount() https://github.com/mongodb/mongo/blob/master/jstests/core/array_match1.js

5) getSisterDB() as an alias for getSiblingDB() https://github.com/mongodb/mongo/blob/master/jstests/core/auth_copydb.js

Plus, added 'explain', 'hint' to cursor.