added check if --download-f2cblaslapack is already specified as petsc arg

Fix for #15 (closed)

In the end, it was not necessary to build the libraries. The problem was that --download-f2cblaslapack=1 is always set, if --download-ptscotch is a PETSc argument. If blaslapack is downloaded then it seems that the libraries in the MKL folder are ignored.