Fixed pretty-printing of strings in the string container.

[marek-trtik]

Unfortutatelly, the solution with a single free function
does not work. GCC seams to ignore attributes and throws
the function away. Fortunatelly, it does not ignore
attributes, when given to non-static method, and so
the non-debug build can be as fast as before.

Here is the pretty-printer function for QTCreator:

def qdump__dstringt(d, value):
    try:
        address = address_of_value(value)
        string_no = str(gdb.parse_and_eval("(*((const dstringt*)" + address + ")).no"))
        has_no = str(gdb.parse_and_eval("get_string_container().is_number_valid(" + string_no +")"))
        if has_no == "true":
            raw_string_value = str(gdb.parse_and_eval("get_string_container().get_string_slowly(" + string_no +")"))
            string_value = raw_string_value.replace("\0", "").replace("\"", "\\\"")
            d.putValue(string_no + ": " + string_value)
        else:
            d.putValue(string_no + ": The number is invalid.")
    except Exception as e:
        d.putValue("Exception getting value of dstringt: " + str(e))

[peterschrammel]

This should rather go into cbmc/develop directly.