Feature: explicit string representation for enum fields

tests/accept/run/tenumhole.nim

@@ -0,0 +1,16 @@
+
+const
+  strValB = "my value B"
+
+type
+  TMyEnum = enum
+    valueA = (1, "my value A"),
+    valueB = strValB & "conc",
+    valueC,
+    valueD = (4, "abc")
+ 
+# trick the optimizer with a variable:
+var x = valueD
+echo valueA, ord(valueA), valueB, ord(valueB), valueC, valueD, ord(valueD), x
+
+