PLCObject got more methods serialized through worker : Start, Stop, NewPLC.
This particularly helps with initialization/startup/re-load problems
when targeting Xenomai. It should help in general for runtime robustness,
since those operations aren't meant to be executed concurrently.

          <xsd:attribute name="Command" type="xsd:string" use="optional" default="make -C %(buildpath)s all BEREMIZSRC=%(src)s BEREMIZCFLAGS=%(cflags)s MD5=%(md5)s USE_BEREMIZ=1 FROM_BEREMIZ=1"/>