RUNTIME: Variable trace now uses limited list and buffer instead of flags in instance tree that was requiring systematical instance tree traversal, and worst size buffer. Forcing and retain still use tree traversal.

          <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"/>