Refactor environment setup.

- Gave setup_environment and setup_dependent_environment more similar
  signatures. They now allows editing the Spack env and the runtime
  env for *this* package and dependents, respectively.

- modify_module renamed to setup_dependent_python_module for symmetry
  with setup_dependent_environment and to avoid confusion with
  environment modules.

- removed need for patching Package objects at runtime.

- adjust packages to reflect these changes.

var/spack/repos/builtin/packages/mpich/package.py

@@ -47,13 +47,6 @@ class Mpich(Package):
     provides('mpi@:3.0', when='@3:')
     provides('mpi@:1.3', when='@1:')
 
-    def setup_environment(self, env):
-        env.set_env('MPICH_CC', self.compiler.cc)
-        env.set_env('MPICH_CXX', self.compiler.cxx)
-        env.set_env('MPICH_F77', self.compiler.f77)
-        env.set_env('MPICH_F90', self.compiler.fc)
-        env.set_env('MPICH_FC', self.compiler.fc)
-
     def setup_dependent_environment(self, env, dependent_spec):
         env.set_env('MPICH_CC', spack_cc)
         env.set_env('MPICH_CXX', spack_cxx)
@@ -61,7 +54,7 @@ def setup_dependent_environment(self, env, dependent_spec):
         env.set_env('MPICH_F90', spack_f90)
         env.set_env('MPICH_FC', spack_fc)
 
-    def modify_module(self, module, spec, dep_spec):
+    def setup_dependent_python_module(self, module, spec, dep_spec):
         """For dependencies, make mpicc's use spack wrapper."""
         # FIXME : is this necessary ? Shouldn't this be part of a contract with MPI providers?
         module.mpicc = join_path(self.prefix.bin, 'mpicc')