Fix Debian bug #463322: Use deprecated libldap API

Fix Debian bug #463322: Use deprecated libldap API

| Our automated build log filter[1] detected a problem that is likely to
| cause your package to segfault on architectures where the size of a
| pointer is greater than the size of an integer, such as ia64 and
| amd64.
|
| This is often due to a missing function prototype definition.  For
| more information, see [2].
|
| 	Function `ldap_init' implicitly converted to pointer at
| 	check_ldap.c:124
|
| [1] http://people.debian.org/~dannf/check-implicit-pointer-functions
| [2] http://wiki.debian.org/ImplicitPointerConversions
|
| The libldap API has been updated and many functions used by the ldap
| plugin are now deprecated.  This package should either update to the
| new API or define LDAP_DEPRECATED to continue using the deprecated
| interfaces.
|
| This patch implements the lazy solution.

[ http://bugs.debian.org/463322 ]

(Contributed by Dann Frazier, forwarded by Jan Wagner.)