fix typos

activerecord/lib/active_record/callbacks.rb

@@ -83,7 +83,7 @@ module ActiveRecord
   #
   # In that case, <tt>Reply#destroy</tt> would only run +destroy_readers+ and _not_ +destroy_author+.
   # So, use the callback macros when you want to ensure that a certain callback is called for the entire
-  # hierarchy, and use the regular overwriteable methods when you want to leave it up to each descendant
+  # hierarchy, and use the regular overwritable methods when you want to leave it up to each descendant
   # to decide whether they want to call +super+ and trigger the inherited callbacks.
   #
   # *IMPORTANT:* In order for inheritance to work for the callback queues, you must specify the

activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

@@ -383,7 +383,7 @@ def type_cast(value)
 
         TYPES = {}
 
-        # Register an MySQL +type_id+ with a typcasting object in
+        # Register an MySQL +type_id+ with a typecasting object in
         # +type+.
         def self.register_type(type_id, type)
           TYPES[type_id] = type