Introduce MDB_BACKEND_* enum

include/mdbtools.h

@@ -190,6 +190,15 @@ enum {
 typedef struct mdbindex MdbIndex;
 typedef struct mdbsargtree MdbSargNode;
 
+enum {
+	MDB_BACKEND_ACCESS = 1,
+	MDB_BACKEND_ORACLE,
+	MDB_BACKEND_SYBASE,
+	MDB_BACKEND_POSTGRES,
+	MDB_BACKEND_MYSQL,
+	MDB_BACKEND_SQLITE,
+};
+
 typedef struct {
 	char *name;
 	unsigned char needs_length; /* or precision */