[petsc-dev] --with-package --download-package options on Windows

[Barry Smith]

    Because I got sick of people using various --download-package on  
Windows that does not work I have made the following additions to  
package.py

   worksonWindows and downloadonWindows which by default are set to 0;  
i.e. does not work.

   I turn the worksonWindows for MPI and the worksonWindows and  
downloadonWindows for BlasLapack

   If they are false and user tries to use them it should print a nice  
message saying why the don't work.

   Please adjust the flags in any package.py where they do work by  
setting the appropriate values to 1.

   I have not tested this on Windows.

    Barry

   I see the checks are already there for --download-mpich and -- 
download-openmpi. Good.