changes to plapack usage in petsc-dev

[Barry Smith]

   petsc-dev users,

    I have changed the way PLAPACK is used in petsc-dev. There is no  
longer
a MATPLAPACK that needs to be set, rather so long as PETS was config/ 
configure.py
using --download-plapack all you need do is use the MATMPIDENSE matrices
and PLAPACK will automatically be used for the solvers.

    Barry

You should rm the externalpackages/plapack* routine before config/ 
configure.py the latest
Petsc-dev