SERVER-11792 Fixed mongos option help to specify size units

Signed-off-by: Matt Kangas <matt.kangas@mongodb.com>
SERVER-10026 mock stage doesn't copy WSMs anymore but instead the data inside
SERVER-11792 fix mongos_options_test
SERVER-10566 WorkingSet cleanup and optimization

Changes:

* Documented some contracts
* Marked noncopyable classes as such
* Changed WorkingSetID to size_t from long
* Inlined WorkingSet::get since it is simple and very hot
* WorkingSetMembers are now pooled and reused
* Stopped using unordered_(map|set)
** _data became a vector with freelist
** _flagged became a bool on each member of _data
** _computed became an embedded array
SERVER-11781 Don't crash when converting deeply nested or cyclical JS objects to BSON
SERVER-11781 Use enum hack to avoid need to assign storage to static constant
SERVER-7973: when fsyncing the data files to disk, do not hold any locks
SERVER-11827 Make changeOwnPassword privilege target the user's database rather than the cluster
SERVER-11781 better fix for V8Scope::objectDeptLimit linker error
SERVER-10566 Don't use modulus in ElapsedTracker
SERVER-11414 added test cases for null comparison operations on non-existent fields
SERVER-11422 added test cases for null comparison
setup_multiversion_mongodb.py no longer refers to nonexistent install_multiversion_mongodb.sh

Signed-off-by: Matt Kangas <matt.kangas@mongodb.com>