PROTON-232: described arrays seem to force the descriptor to be of the same type as the array

Fixed bug in code.c pn_data_encode_node: was always using the parent->type
for everything inside an array, including the descriptor.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1447943 13f79535-47bb-0310-9956-ffa450edef68