Integrate https://github.com/10gen/mongo/tree/anna.wawrzyniak/profiler with mongod in master branch.

The tracing profiler allows to manually mark scopes/regions in the code and then precisely measure (cycle clock precision) the time spent and invocation count for each region. It also supports nested regions/scopes 

This tracing profiler aggregates the measurements, without storing all traces.

The metrics are available via regular mongod stats.