Create a new extension type WT_STRESSOR for use with stress testing.  The initial one can be configured (and reconfigured, at runtime) to create and maintain a certain number of active dhandles.  Such a plug-in can be easily added via wiredtiger_open config to add a new stressor to test/format or wtperf or workgen, without adding any code to them.  (To take advantage of reconfiguring at runtime, I think workgen will need a little bit of code changes, that's well worth it for creating some flexible benchmarks).  It will add a new dimension to testing and benchmarking, and set the stage for adding additional stressors in the future.