Implements extended error messages

This commit introduces a new constant that can be used to retrieve more
detailed error messages.

This fixes #47222

The new constant LDAP_OPT_DIAGNOSTIC_MESSAGE is defined in PHP when the
underlying library provides (and understands) it. This is the case in
the current OpenLDAP-implementation.

Tanks to Johnny Willer who provided the solution at http://stackoverflow.com/questions/28765077/get-number-of-ad-errors-with-ldap-and-php-ldap-function-return-unprecise-error/28816473#28816473

ext/ldap/ldap.c

@@ -191,6 +191,10 @@ PHP_MINIT_FUNCTION(ldap)
 	REGISTER_LONG_CONSTANT("LDAP_OPT_DEBUG_LEVEL", LDAP_OPT_DEBUG_LEVEL, CONST_PERSISTENT | CONST_CS);
 #endif
 
+#ifdef LDAP_OPT_DIAGNOSTIC_MESSAGE
+	REGISTER_LONG_CONSTANT("LDAP_OPT_DIAGNOSTIC_MESSAGE", LDAP_OPT_DIAGNOSTIC_MESSAGE, CONST_PERSISTENT | CONST_CS);
+#endif
+
 #ifdef HAVE_LDAP_SASL
 	REGISTER_LONG_CONSTANT("LDAP_OPT_X_SASL_MECH", LDAP_OPT_X_SASL_MECH, CONST_PERSISTENT | CONST_CS);
 	REGISTER_LONG_CONSTANT("LDAP_OPT_X_SASL_REALM", LDAP_OPT_X_SASL_REALM, CONST_PERSISTENT | CONST_CS);