feat(sdam): backport unified SDAM changes from next to master

The unified SDAM will be shipped in v3.2.0 now, so this brings the
changes over the past four months into `master` for that release.

Author: mbroadst

index.js

@@ -33,6 +33,7 @@ module.exports = {
   Sessions: require('./lib/sessions'),
   BSON: BSON,
   EJSON: EJSON,
+  Topology: require('./lib/sdam/topology'),
   // Raw operations
   Query: require('./lib/connection/commands').Query,
   // Auth mechanisms

lib/connection/connect.js

@@ -108,7 +108,7 @@ function performInitialHandshake(conn, options, callback) {
         options.port +
         ' reports wire version ' +
         (ismaster.maxWireVersion || 0) +
-        ', but this version of Node.js Driver requires at least ' +
+        ', but this version of the Node.js Driver requires at least ' +
         latestSupportedMaxWireVersion +
         ' (MongoDB' +
         latestSupportedVersion +