Backport:
MissingIgnoreFromData does not work, and corrupts server (test + fix)

git-svn-id: https://svn.apache.org/repos/asf/ode/trunk@966143 13f79535-47bb-0310-9956-ffa450edef68
ODE-380: Message#setHeaderPart should overwrite any previous value
Thanks to William McCusker for the patch.