Diagnostics Shell Helper diag.checkFragmentation()

This helper function would compare a number of database statistics from db.stats() and output a report highlighting where potential fragmentation might exist. This information could indicate when a repair / compact on a database / collection is necessary.

The implementation should produce machine readable and useable versions as well as a textual report.

Motivation:
The idea is to identify if a database may have fragmentation by applying a number of rules of thumb to the various db.stats() - essentially a quick indicator that fragmentation may exist and that it is appropriate to perform maintenance on the mongod. This is straight forward when dealing with a single host, however suffers when it needs to be scaled up to dozens / hundreds of hosts.