Startup code

[rfoxkendo]

• Make SpecTcl understand MPI builds via configuration options:
  • --enable-mpi - turns on WITH_MPI in config.h
  • --with-mpicc - Sets path to the mpicc compiler.
  • --with-mpicxx - sets path to the mpicxx compiler
• Make the start up code do different things if it's under mpirun with the mpi enabled than it would in serial mode.