Add changelog entry for #9203 about schema dumper with db extensions

[ci skip]

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Schema dumper supports dumping the enabled database extensions to `schema.rb`
+    (currently only supported by postgresql).
+
+    *Justin George*
+
 *   The `DATABASE_URL` environment variable now converts ints, floats, and
     the strings true and false to Ruby types. For example, SQLite requires
     that the timeout value is an integer, and PostgreSQL requires that the

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -178,7 +178,7 @@ def supports_extensions?
       end
 
       # A list of extensions, to be filled in by databases that
-      # support them (at the moment, postgresql)
+      # support them (at the moment, postgresql).
       def extensions
         []
       end
@@ -186,7 +186,7 @@ def extensions
       # QUOTING ==================================================
 
       # Returns a bind substitution value given a +column+ and list of current
-      # +binds+
+      # +binds+.
       def substitute_at(column, index)
         Arel::Nodes::BindParam.new '?'
       end