bugfix: env.write() should stringify Spec lists.

- Setting specs from lockfiles was not correctly stringifying concretized
  user specs.

- Fix `_set_user_specs_from_lockfile`

- Add some validation code to `SpecList` constructor

lib/spack/spack/environment.py

@@ -600,8 +600,8 @@ def _set_user_specs_from_lockfile(self):
         """Copy user_specs from a read-in lockfile."""
         self.spec_lists = {
             user_speclist_name: SpecList(
-                user_speclist_name, [Spec(s)
-                                     for s in self.concretized_user_specs]
+                user_speclist_name,
+                [str(s) for s in self.concretized_user_specs]
             )
         }
 

lib/spack/spack/spec_list.py

@@ -28,6 +28,12 @@ def __init__(self, name='specs', yaml_list=[], reference={}):
         self.name = name
         self._reference = reference  # TODO: Do we need defensive copy here?
 
+        # Validate yaml_list before assigning
+        if not all(isinstance(s, string_types) or isinstance(s, (list, dict))
+                   for s in yaml_list):
+            raise ValueError(
+                "yaml_list can contain only valid YAML types!  Found:\n  %s"
+                % [type(s) for s in yaml_list])
         self.yaml_list = yaml_list[:]
 
         # Expansions can be expensive to compute and difficult to keep updated