Fixed LDAP library file name bug (KNOWN_BUGS #1). configure now auto-detects

the correct dynamic library names by default, and provides override switches
--with-ldap-lib, --with-lber-lib and --without-lber-lib.  Added
CURL_DISABLE_LDAP to platform-specific config files to disable LDAP
support on those platforms that probably don't have dynamic OpenLDAP
libraries available to avoid compile errors.