[Scalapack] building BLACS on mac osx

[Ed D'Azevedo]

The file system on mac osx is not case sensitive so file.C is the  
same as file.c.

This makes it difficult to build BLACS correctly since BLACS uses  
".C" as object code produced by C code.

A simple work around might be modifying the makefile (say under SRC/ 
MPI) to use another suffix say  ".X" instead of ".C".

Just a suggestion.