Thrift: Slight tweaks to local reflection.

Thrift: Slight tweaks to local reflection.

Summary:
Local reflection typespecs for structs now have a dummy T_STOP field at the end
so we don't have to check the size on every iteration.
They also contain information about which fields are optional.
Also put a static pointer to the reflection in each structure.

Reviewed By: mcslee

Test Plan: test/DenseLinkingTest.thrift

Revert Plan: ok

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665246 13f79535-47bb-0310-9956-ffa450edef68