1. Prevent from errors when the host is configured e.g. with ldap:// prefix
2. Use sys_get_temp_dir() to get the system tmp directory

This reverts commit 0ba431be.

Summary:
This change will allow the package to be submitted to packagist.org
for easy installation via Composer.

Reviewers: vanmeeuwen, machniak

Reviewed By: machniak

Subscribers: bruederli

Differential Revision: https://git.kolab.org/D121

Remove unused variable, remove @ on ldap_add(), this may print useful warnings that are not related to ldap connection

Summary:
recursive deletion: need to find and delete objects with objectclass ldapsubentry as well (#5100).
This is for example needed when deleting a domain, for the role kolab-admin which has class ldapsubentry

Reviewers: vanmeeuwen, #web_administration_panel_developers

Reviewed By: vanmeeuwen, #web_administration_panel_developers

Subscribers: machniak, vanmeeuwen

Differential Revision: https://git.kolab.org/D23

Resolves T135

Also provide caching handler and cleanup some debug messages.
Most of the code moved from Kolab WebAdmin.

ldap_search() throws errors on empty filter as find out in
http://trac.roundcube.net/ticket/1490269. As this was a configuration
issue we can simply prevent that and provide real and working default.