Improve readability of base output in debugging.

Also, output UNKNOWN_PREFIX ('?') instead of writing a nul character
when the attribute prefix is unknown.

servers/slapd/back-ldbm/back-ldbm.h

@@ -29,6 +29,8 @@ LDAP_BEGIN_DECL
 #define SUB_PREFIX	'*'	/* prefix for substring keys    */
 #define CONT_PREFIX	'\\'	/* prefix for continuation keys */
 
+#define UNKNOWN_PREFIX	'?'	/* prefix for unknown keys    */
+
 #define DEFAULT_BLOCKSIZE	8192
 
 /*

servers/slapd/back-ldbm/index.c

@@ -129,7 +129,7 @@ index_read(
 
 	realval = val;
 	tmpval = NULL;
-	if ( prefix != '\0' ) {
+	if ( prefix != UNKNOWN_PREFIX ) {
               unsigned int	len = strlen( val );
 
               if ( (len + 2) < sizeof(buf) ) {
@@ -185,7 +185,7 @@ add_value(
 	realval = val;
 	tmpval = NULL;
 	idl = NULL;
-	if ( prefix != '\0' ) {
+	if ( prefix != UNKNOWN_PREFIX ) {
               unsigned int     len = strlen( val );
 
               if ( (len + 2) < sizeof(buf) ) {
@@ -359,7 +359,7 @@ index2prefix( int indextype )
 		prefix = SUB_PREFIX;
 		break;
 	default:
-		prefix = '\0';
+		prefix = UNKNOWN_PREFIX;
 		break;
 	}
 

servers/slapd/back-ldbm/search.c

@@ -87,7 +87,7 @@ ldbm_back_search(
 
 	(void) dn_normalize (realBase);
 
-	Debug( LDAP_DEBUG_TRACE, "using base %s\n",
+	Debug( LDAP_DEBUG_TRACE, "using base \"%s\"\n",
 		realBase, 0, 0 );
 
 	switch ( scope ) {
@@ -323,7 +323,7 @@ base_candidates(
 	IDList		*idl;
 	Entry		*e;
 
-	Debug(LDAP_DEBUG_TRACE, "base_candidates: base: %s\n", base, 0, 0);
+	Debug(LDAP_DEBUG_TRACE, "base_candidates: base: \"%s\"\n", base, 0, 0);
 
 	*err = LDAP_SUCCESS;
 
@@ -364,7 +364,7 @@ onelevel_candidates(
 	char		buf[20];
 	IDList		*candidates;
 
-	Debug(LDAP_DEBUG_TRACE, "onelevel_candidates: base: %s\n", base, 0, 0);
+	Debug(LDAP_DEBUG_TRACE, "onelevel_candidates: base: \"%s\"\n", base, 0, 0);
 
 	*err = LDAP_SUCCESS;
 	e = NULL;
@@ -425,8 +425,8 @@ subtree_candidates(
 	Filter		*f, **filterarg_ptr;
 	IDList		*candidates;
 
-	Debug(LDAP_DEBUG_TRACE, "subtree_candidates: base: %s\n",
-		base ? base : "NULL", 0, 0);
+	Debug(LDAP_DEBUG_TRACE, "subtree_candidates: base: \"%s\" %s\n",
+		base ? base : "NULL", lookupbase ? "lookupbase" : "", 0);
 
 	/*
 	 * get the base object - unless we already have it (from one-level).