Fix for issue #60

The problem reported in issue #60 occurs when a user downloads an
archive of Distiller instead of performing "git clone".
When downloading an archive there is no ".git" directory and we
need to handle this gracefully.
For more details, see the issue itself.

apputils/execution_env.py

@@ -28,7 +28,7 @@ import logging
 import logging.config
 import numpy as np
 import torch
-from git import Repo
+from git import Repo, InvalidGitRepositoryError
 HAVE_LSB = True
 try:
     import lsb_release
@@ -53,11 +53,15 @@ def log_execution_env_state(app_args, gitroot='.'):
 
         It is useful to know what git tag we're using, and if we have outstanding code.
         """
-        repo = Repo(gitroot)
-        assert not repo.bare
+        try:
+            repo = Repo(gitroot)
+            assert not repo.bare
+        except InvalidGitRepositoryError:
+            logger.debug("Cannot find a Git repository.  You probably downloaded an archive of Distiller.")
+            return
 
         if repo.is_dirty():
-            logger.debug("Git is dirty")
+           logger.debug("Git is dirty")
         try:
             branch_name = repo.active_branch.name
         except TypeError: