Fixed #9253 -- Modified the method used to generate constraint names so that...

Fixed #9253 -- Modified the method used to generate constraint names so that it is consistent regardless of machine word size.

NOTE: This change is backwards incompatible for some users.

If you are using a 32-bit platform, you will observe no differences as a
result of this change. However, users on 64-bit platforms may experience
some problems using the `reset` management command.

Prior to this change, 64-bit platforms would generate a 64-bit, 16 character
digest in the constraint name; for example:

ALTER TABLE `myapp_sometable` ADD CONSTRAINT `object_id_refs_id_5e8f10c132091d1e` FOREIGN KEY ...

Following this change, all platforms, regardless of word size, will
generate a 32-bit, 8 character digest in the constraint name; for example:

ALTER TABLE `myapp_sometable` ADD CONSTRAINT `object_id_refs_id_32091d1e` FOREIGN KEY ...

As a result of this change, you will not be able to use the `reset`
management command on any table created with 64-bit constraints. This
is because the the new generated name will not match the historically
generated name; as a result, the SQL constructed by the `reset` command
will be invalid.

If you need to reset an application that was created with 64-bit
constraints, you will need to manually drop the old constraint prior
to invoking `reset`.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10966 bcc190cf-cafb-0310-a4f2-bffc1f526a37