Ensure associations doesn't table name collide with string joins

Currently we have no test for alias tracking with string joins. I've add
test case for that to catch a future regression.

activerecord/lib/active_record/associations/alias_tracker.rb

@@ -19,14 +19,16 @@ def self.create(connection, initial_table, joins)
       end
 
       def self.initial_count_for(connection, name, table_joins)
-        # quoted_name should be downcased as some database adapters (Oracle) return quoted name in uppercase
-        quoted_name = connection.quote_table_name(name).downcase
+        quoted_name = nil
 
         counts = table_joins.map do |join|
           if join.is_a?(Arel::Nodes::StringJoin)
+            # quoted_name should be case ignored as some database adapters (Oracle) return quoted name in uppercase
+            quoted_name ||= connection.quote_table_name(name)
+
             # Table names + table aliases
-            join.left.downcase.scan(
-              /join(?:\s+\w+)?\s+(\S+\s+)?#{quoted_name}\son/
+            join.left.scan(
+              /JOIN(?:\s+\w+)?\s+(?:\S+\s+)?(?:#{quoted_name}|#{name})\sON/i
             ).size
           elsif join.respond_to? :left
             join.left.table_name == name ? 1 : 0

activerecord/test/cases/associations/inner_join_association_test.rb

@@ -27,6 +27,11 @@ def test_construct_finder_sql_does_not_table_name_collide_on_duplicate_associati
     end
   end
 
+  def test_construct_finder_sql_does_not_table_name_collide_with_string_joins
+    sql = Person.joins(:agents).joins("JOIN people agents_people ON agents_people.primary_contact_id = people.id").to_sql
+    assert_match(/agents_people_2/i, sql)
+  end
+
   def test_construct_finder_sql_ignores_empty_joins_hash
     sql = Author.joins({}).to_sql
     assert_no_match(/JOIN/i, sql)