Handle OP_STRING in dump_subexp_body_standard

For some reason, OP_STRING is not handled in dump_subexp_body_standard.
This makes the output of "set debug expression 1" very bad when a string
is involved. Example:

(gdb) set debug expression 1
(gdb) print "hello"
... (random garbage, possibly segfault)

This commit handles OP_STRING and skips the appropriate number of exp
elements. The line corresponding to the string now looks like:

	    0  OP_STRING             Language-specific string type: 0

gdb/ChangeLog:

2014-07-15  Simon Marchi  <simon.marchi@ericsson.com>

	* expprint.c (dump_subexp_body_standard): Handle OP_STRING.

gdb/ChangeLog

+2014-07-15  Simon Marchi  <simon.marchi@ericsson.com>
+
+	* expprint.c (dump_subexp_body_standard): Handle OP_STRING.
+
 2014-07-14  Edjunior Barbosa Machado  <emachado@linux.vnet.ibm.com>
 
 	* ppc-linux-nat.c (ppc_linux_can_use_hw_breakpoint): Report no hardware

gdb/expprint.c

@@ -1011,12 +1011,29 @@ dump_subexp_body_standard (struct expression *exp,
 	elt = dump_subexp (exp, stream, elt);
       }
       break;
+    case OP_STRING:
+      {
+	LONGEST len = exp->elts[elt].longconst;
+	LONGEST type = exp->elts[elt + 1].longconst;
+
+	fprintf_filtered (stream, "Language-specific string type: %s",
+			  plongest (type));
+
+	/* Skip length.  */
+	elt += 1;
+
+	/* Skip string content. */
+	elt += BYTES_TO_EXP_ELEM (len);
+
+	/* Skip length and ending OP_STRING. */
+	elt += 2;
+      }
+      break;
     default:
     case OP_NULL:
     case MULTI_SUBSCRIPT:
     case OP_F77_UNDETERMINED_ARGLIST:
     case OP_COMPLEX:
-    case OP_STRING:
     case OP_BOOL:
     case OP_M2_STRING:
     case OP_THIS: