Call libMesh::write_traceout() in mooseError(), mooseAssert()

This is a no-op unless you configure libmesh with --enable-tracefiles.
Without this, you don't get a stack trace from mooseError/Assert() in
parallel.

Refs #4398
Merge pull request #4399 from jwpeterson/write_traceout

Call libMesh::write_traceout() in mooseError(), mooseAssert()