libapl installation

[Chris Moller]

    Hi, Jürgen,
      
      I hate to be a nuisance, but would it be possible, when installing
      libapl.h to simultaneously install ErrorCode.hh and Error.def in
      the same place?  apl_exec() and apl_exec_ucs() in libapl.cc can
      return those codes.  
      
      Thanks,
      Chris