Add 'nibbles' to gdb.print_options

When I rebased and updated the print_options patch, I forgot to update
print_options to add the new 'nibbles' feature to the result.  This
patch fixes the oversight.  I'm checking this in.

gdb/python/py-prettyprint.c

@@ -753,6 +753,8 @@ gdbpy_print_options (PyObject *unused1, PyObject *unused2)
 		      opts.static_field_print) < 0
       || set_boolean (result.get (), "deref_refs",
 		      opts.deref_ref) < 0
+      || set_boolean (result.get (), "nibbles",
+		      opts.nibblesprint) < 0
       || set_boolean (result.get (), "summary",
 		      opts.summary) < 0
       || set_unsigned (result.get (), "max_elements",