setup_extension_environment is now setup_dependent_environment.

- other packages, like Qt, can now use this to set up relevant build
  variables and env vars for their dependencies.

- not just extensions anymore.

lib/spack/spack/package.py

@@ -829,10 +829,10 @@ def do_install(self, **kwargs):
                 self.stage.chdir_to_source()
                 build_env.setup_package(self)
 
-                # Allow extendees to further set up the environment.
-                if self.is_extension:
-                    self.extendee_spec.package.setup_extension_environment(
-                        self.module, self.extendee_spec, self.spec)
+                # Allow dependencies to further set up the environment.
+                for dep_spec in self.spec.traverse(root=False):
+                    dep_spec.package.setup_dependent_environment(
+                        self.module, dep_spec, self.spec)
 
                 if fake_install:
                     self.do_fake_install()
@@ -910,8 +910,8 @@ def module(self):
                           fromlist=[self.__class__.__name__])
 
 
-    def setup_extension_environment(self, module, spec, ext_spec):
-        """Called before the install() method of extensions.
+    def setup_dependent_environment(self, module, spec, dependent_spec):
+        """Called before the install() method of dependents.
 
         Default implementation does nothing, but this can be
         overridden by an extendable package to set up the install
@@ -930,6 +930,8 @@ def setup_extension_environment(self, module, spec, ext_spec):
            put a 'python' Execuable object in the module scope for the
            extension package to simplify extension installs.
 
+        3. A lot of Qt extensions need QTDIR set.  This can be used to do that.
+
         """
         pass