[ysh translation] Fix int literal bug by removing 0b 0o 0x prefixes

Python allows int('0b10', 2), but we don't.

spec/ysh-command-sub.test.sh

@@ -1,7 +1,6 @@
 ## oils_failures_allowed: 1
 
-
-#### conflict with extglob @( cna be avoided with ,(
+#### Conflict with extglob @( can be avoided with ,(
 
 shopt -s extglob
 

ysh/expr_eval.py

@@ -392,11 +392,14 @@ def _EvalConst(self, node):
         if id_ == Id.Expr_DecInt:
             return value.Int(int(c_under))
         if id_ == Id.Expr_BinInt:
-            return value.Int(int(c_under, 2))
+            assert c_under[:2] in ('0b', '0B'), c_under
+            return value.Int(int(c_under[2:], 2))
         if id_ == Id.Expr_OctInt:
-            return value.Int(int(c_under, 8))
+            assert c_under[:2] in ('0o', '0O'), c_under
+            return value.Int(int(c_under[2:], 8))
         if id_ == Id.Expr_HexInt:
-            return value.Int(int(c_under, 16))
+            assert c_under[:2] in ('0x', '0X'), c_under
+            return value.Int(int(c_under[2:], 16))
 
         if id_ == Id.Expr_Float:
             # Note: float() in mycpp/gc_builtins.py currently uses strtod