Read a per-user mailbox_command from LDAP
scriptsMailboxCommand is currently generated as an operational
attribute using the following CoS template in LDAP:
dn: cn=scriptsMailboxCommandTemplate,ou=People,dc=scripts,dc=mit,dc=edu
cn: scriptsMailboxCommandTemplate
objectClass: top
objectClass: cosTemplate
objectClass: extensibleObject
scriptsmailboxcommand: /usr/bin/procmail -t -p -a "${EXTENSION}" ~/mail_scripts/procmailrc
dn: cn=scriptsMailboxCommandCoS,ou=People,dc=scripts,dc=mit,dc=edu
cn: scriptsMailboxCommandCoS
objectClass: top
objectClass: ldapSubEntry
objectClass: cosSuperDefinition
objectClass: cosPointerDefinition
costemplatedn: cn=scriptsMailboxCommandTemplate,ou=People,dc=scripts,dc=mit,dc=edu
cosAttribute: scriptsMailboxCommand operational-default
