stopped adding system.users indexes to catalog twice #527
SERVER-8429 Fix tests in jstests/tool.

The affected tests depended on a behavior of mongodump and mongorestore in 2.2
and prior, whereby the tools would attempt authentication via the users'
credentials against several databases, until one matched.  This behavior is
risky, because it could leave the tool authenticating as a user with
insufficient privilege to do its task, and it is inconsistent with other tools.

The tool behavior in 2.4 is to authenticate against the target database if one
is supplied, or admin if none is supplied, unless the user overrides this
behavior by passing --authenticationDatabase=dbname to the tool.
SERVER-7864 Disable jstests/auth/copyauth.js test as copyDatabase no longer works with auth
Clarify comment about the internal separation of read-only and read-write system roles
SERVER-7864 Make copyDB, clone, and cloneCollection work with auth.

copyDB and clone can only be run when auth is enabled if the client is
authenticated as an old-style user. New style users using the extended form
privilege documents cannon run copyDB or clone when auth is enabled.  They can
still run cloneCollection (against the target instance), so long as the source
instance doesn't have auth on.

Conflicts:
	src/mongo/db/cloner.cpp