Fix script to cope with latest ASN1SCC

CHOICE type now have a separate _selection type for the choice
discriminant. This broke the script that extracted the constants from
the .h file generated by asn1scc

dmt/A_mappers/learn_CHOICE_enums.py

@@ -15,10 +15,13 @@ There is no name clash thanks to the rename policy of the ASN.1 compiler
 for line in open(sys.argv[1] + '.h', 'r'):
     if '_PRESENT' in line and not line.startswith('#define'):
         choices.append(line.strip().replace(",", ""))
+        bEnum = False
     elif line.strip().startswith('typedef enum {'):
         bEnum = True
     elif line.strip().startswith('}') and bEnum:
         bEnum = False
+    elif '_NONE' in line or '_PRESENT' in line:
+        bEnum = False
     elif bEnum:
         enums.append(line.strip().replace(",", "").split("="))