[krbdev.mit.edu #4292] LDAP error prevents KfM 6.0 from building on Tiger

[Alexandra Ellwood via RT]

On Tiger I now get: 
plugins/kdb/ldap/libkdb_ldap/kdb_ldap.h:42:4: error: #error This code triggers bugs in old 
OpenLDAP implementations. Please update to 2.2.24 or later.

I realize that the LDAP plugin can't support Tiger's LDAP 2.2.19, but I'd like to be able to do 
development of KfM 6.0 on Tiger.

#warning works on all Mac OS X compilers.  So if you special case this for Mac OS X, you can 
add a #warning so it continues to warn about the problem.  Alternatively a macro to skip the 
#error would be fine as well.