- added a test which tries to compile, link and run a sample program

  with the default compiler and the flags extracted from the different
  mpicc-scripts. If it fails a warning is emitted and MPI deactivated

  fixes bug #23

- added theoretical support for GCC with IBM MPI: the options (which
  are tailored toward xlc) are changed a bit. However the following
  problem remains: ./configure adapts the test programs to the
  C++ compiler it find. Thus, a test program passed to mpCC fails
  because the implicitly used xlC doesn't understand the line meant
  for g++... Maybe this (and a whole lot of other problems) just
  vanish if xlc 7.0 is used so I'll do nothing about it

[[Imported from SVN: r2412]]