Description of problem:
If ldap(AD)'s structure is like this:
===

• com
• sample
• Business Unit 1
• Subunit 1.1
• user 1
• user 2
• Business Unit 2
• Subunit 2.1
• user 3
  ===
  we can not find all of users in this structure by Using appropriate base DN, "com.sample", because default search scope used by LDAPUserGroupCallbackImpl is "one"[1]. Therefore, setting base DN to the root DN does not work.

Although we can use a custom LDAPUserGroupCallbackImpl, this is a common use case for ldap search, so I report it as bug.

[1] Default is search one level
http://docs.oracle.com/javase/7/docs/api/javax/naming/directory/SearchControls.html#SearchControls()

Steps to Reproduce:
1. prepare ldap tree like this:
===

• com
• sample
• Business Unit 1
• Subunit 1.1
• user 1
• user 2
• Business Unit 2
• Subunit 2.1
• user 3
  ===
  2. find users

Actual results:
LDAPUserInfoImpl can find either "user 1 and 2" or "user 3"

Expected results:
LDAPUserInfoImpl can find all of users.