Make a copy of spec when resolving it

If a specification has a base that can't be resolved, then an exception
is thrown in the resolve() method, indicating that it should be added to
a retry pile. But we're also modifying that specification in the
resolve_document() method. So when we actually do retry the resolution,
the specification may not be in a good state.

Doing a deep copy of the original specification in resolve_document()
solves all these things.

python/lsst/verify/specset.py

@@ -27,6 +27,7 @@
 from past.builtins import basestring
 
 from collections import OrderedDict
+import copy
 import os
 import re
 
@@ -720,6 +721,10 @@ def resolve_document(self, spec_doc):
            Raised when a document's bases cannot be resolved (an inherited
            `~lsst.validate.base.Specification` cannot be found in the repo).
         """
+        # Create a copy of the spec_doc so that if the resolution is aborted
+        # we haven't modified the original document
+        spec_doc = copy.deepcopy(spec_doc)
+
         # Goal is to process all specifications and partials mentioned in
         # the 'base' field (first in, first out) and merge their information
         # to the spec_doc.