add missing lber library - fixes build on ubuntu 14.04

Missing library on Ubuntu 14.04 fails with this otherwise:
/usr/bin/ld: ldapapi.o: undefined reference to symbol 'ber_free@@OPENLDAP_2.4_2'
//usr/lib/x86_64-linux-gnu/liblber-2.4.so.2: error adding symbols: DSO missing from command line