move fixed-size determination mostly into libdisasm

@@ -43,10 +43,11 @@
         dis_disassemble;
         dis_errno;
         dis_handle_create;
         dis_handle_destroy;
         dis_max_instrlen;
+        dis_min_instrlen;
         dis_previnstr;
         dis_set_data;
         dis_flags_set;
         dis_flags_clear;
         dis_strerror;