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/netlib-scalapack/package.py

@@ -40,7 +40,7 @@ def install(self, spec, prefix):
             make()
             make("install")
 
-    def modify_module(self, module, spec, dependent_spec):
+    def setup_dependent_python_module(self, module, spec, dependent_spec):
         lib_dsuffix = '.dylib' if sys.platform == 'darwin' else '.so'
         lib_suffix = lib_dsuffix if '+shared' in spec['scalapack'] else '.a'