Rename copy.py to avoid stupid Python conflicts

Any other module (in this case, nilmdb -> datetime_tz -> pytz -> gettext)
that does an "import copy" would pull in the copy.py, if it's in the
current working directory.  Python is dumb...

setup.py

@@ -70,7 +70,7 @@ setup(name='nilmtools',
           'console_scripts': [
               'nilm-decimate = nilmtools.decimate:main',
               'nilm-insert = nilmtools.insert:main',
-              'nilm-copy = nilmtools.copy:main',
+              'nilm-copy = nilmtools.copy_:main',
               ],
           },
       zip_safe = False,

src/filter.py

@@ -1,5 +1,7 @@
 #!/usr/bin/python
 
+from __future__ import absolute_import
+
 import nilmdb.client
 from nilmdb.utils.printf import *
 from nilmdb.utils.time import (parse_time, timestamp_to_human,