Update the schema backend to provide full support for online schema updates.
which includes the following:

- It is now possible to add attribute types, objectclasses, name forms, DIT
  content rules, DIT structure rules, and matching rule uses.  Adding a schema
  element that is already present but with a different definition will replace
  that element.

- It is now also possible to remove existing attribute types, objectclasses,
  name forms, DIT content rules, DIT structure rules, and matching rule uses.
  If the element is removed and then re-added, then it is treated as adding the
  element with a a different definition (i.e., replacing the existing
  definition).

- If an existing schema element is replaced or removed, then the update will be
  made in the schema file that contains that definition.  If a new attribute
  type is added and is not manually associated with a schema file, then the
  server will use a default schema file of 99-user.ldif.  The schema file to
  use can be manually overridden using the X-SCHEMA-FILE extension.

- A significant amount of effort has been put into understanding dependencies
  between various schema elements and ensuring that those dependencies will be
  resolved correctly, and will also be updated whenever a dependent element is
  updated.
  
- Note that the equality matching rule for the attributeTypes, objectClasses,
  nameForms, matchingRules, matchingRuleUse, ditContentRules, and 
  ditStructureRules attribute types has been changed to the caseIgnoreMatch
  rule.  This does deviate from the standard somewhat, but allows the server to
  provide notably better performance while still exhibiting correct behavior as
  far as clients are concerned.


OpenDS Issue Number:  366