linux compile options (64-bit)

The problems we are seeing with gcc4 are mainly (but not 
entirely) with gfortran: it seems not quite ready for production use.
-4.0.1 is already a considerable improvement over -4.0.0.

There is another project (www.g95.org) that is using a slightly different 
version of these sources, and either g95 or gfortran can be used with 
gcc3 if you want to use F95 sources.  However, F95 is unlikely to be 
suitable for use in distributed R packages for a long time to come.