Merge pull request #3525 from minrk/utc

Fix basic timezone info

minor tweaks to jsonutil, to include timezone info if available
add IPython.utils.tz, which just has basic info for making utcnow(), etc. include tzinfo in the datetime object
use this tzinfo in the last_modified keys in notebook managers, which fixes Firefox's timezone offset for checkpoints

IPython/html/services/notebooks/filenbmanager.py

@@ -28,6 +28,7 @@ from tornado import web
 from .nbmanager import NotebookManager
 from IPython.nbformat import current
 from IPython.utils.traitlets import Unicode, Dict, Bool, TraitError
+from IPython.utils import tz
 
 #-----------------------------------------------------------------------------
 # Classes
@@ -139,7 +140,7 @@ class FileNotebookManager(NotebookManager):
     def read_notebook_object_from_path(self, path):
         """read a notebook object from a path"""
         info = os.stat(path)
-        last_modified = datetime.datetime.utcfromtimestamp(info.st_mtime)
+        last_modified = tz.utcfromtimestamp(info.st_mtime)
         with open(path,'r') as f:
             s = f.read()
             try:
@@ -281,7 +282,7 @@ class FileNotebookManager(NotebookManager):
         """construct the info dict for a given checkpoint"""
         path = self.get_checkpoint_path(notebook_id, checkpoint_id)
         stats = os.stat(path)
-        last_modified = datetime.datetime.utcfromtimestamp(stats.st_mtime)
+        last_modified = tz.utcfromtimestamp(stats.st_mtime)
         info = dict(
             checkpoint_id = checkpoint_id,
             last_modified = last_modified,