[CMD] Syntax errors during parsing of batch parameters expansion, or FOR and IF commands, are fatal, and batch execution should stop.

- To this purpose use the ParseErrorEx() that correctly sets the
  bParseError flag, and return the partially-parsed command so that
  it gets echoed as well for diagnostics purposes (Windows-compatible).

- Any other parameters specified after (or before) the '/?' switch for
  the FOR and IF commands, are considered fatal syntax errors as well,
  thus we employ the ParseErrorEx() as well.

base/shell/cmd/cmd.c

@@ -1208,7 +1208,7 @@ GetBatchVar(TCHAR *varName, UINT *varNameLen)
         ret = GetEnhancedVar(&varNameEnd, FindArg);
         if (!ret)
         {
-            error_syntax(varName);
+            ParseErrorEx(varName);
             return NULL;
         }
         *varNameLen = varNameEnd - varName;
@@ -1267,6 +1267,14 @@ SubstituteVars(TCHAR *Src, TCHAR *Dest, TCHAR Delim)
         {
             UINT NameLen;
             Var = GetBatchVar(Src, &NameLen);
+            if (!Var && bParseError)
+            {
+                /* Return the partially-parsed command to be
+                 * echoed for error diagnostics purposes. */
+                APPEND1(Delim);
+                APPEND(Src, DestEnd-Dest);
+                return FALSE;
+            }
             if (Var != NULL)
             {
                 VarLength = _tcslen(Var);

base/shell/cmd/for.c

@@ -44,7 +44,7 @@ INT cmd_for(LPTSTR param)
         return 0;
     }
 
-    error_syntax(param);
+    ParseErrorEx(param);
     return 1;
 }
 

base/shell/cmd/if.c

@@ -59,7 +59,7 @@ INT cmd_if(LPTSTR param)
         return 0;
     }
 
-    error_syntax(param);
+    ParseErrorEx(param);
     return 1;
 }