Add configuration to select the original unpatched BASIC

The idea is to use this setting to as far as possible replicate the original BASIC and to turn it off to be able to apply bugfixes or optimizations.

src/,,config_testing_38K.s

@@ -105,6 +105,7 @@
 
 ; --- BASIC features
 
+;; #CONFIG# ORIGINAL_UNPATCHED_BASIC   YES
 ;; #CONFIG# TRANSCENDENTAL_FUNCTIONS   YES