Improve the performance of quoting table names on PG

This caused a pretty major performance regression for 4.2, as this is a
hotspot for query construction. We're still slightly slower than 4.1,
but it's much less significant.

activerecord/lib/active_record/connection_adapters/postgresql/utils.rb

@@ -18,7 +18,11 @@ def to_s
        end

        def quoted
          parts.map { |p| PGconn.quote_ident(p) }.join SEPARATOR
          if schema
            PGconn.quote_ident(schema) << SEPARATOR << PGconn.quote_ident(identifier)
          else
            PGconn.quote_ident(identifier)
          end
        end

        def ==(o)
@@ -32,8 +36,11 @@ def hash

        protected
          def unquote(part)
            return unless part
            part.gsub(/(^"|"$)/,'')
            if part && part.start_with?('"')
              part[1..-2]
            else
              part
            end
          end

          def parts
@@ -57,7 +64,11 @@ module Utils # :nodoc:
        # * <tt>"schema_name".table_name</tt>
        # * <tt>"schema.name"."table name"</tt>
        def extract_schema_qualified_name(string)
          table, schema = string.scan(/[^".\s]+|"[^"]*"/)[0..1].reverse
          schema, table = string.scan(/[^".\s]+|"[^"]*"/)
          if table.nil?
            table = schema
            schema = nil
          end
          PostgreSQL::Name.new(schema, table)
        end
      end