Change print statements to work in python3

This is part of a series of changes to introduce Python3 support.

Change-Id: I373be5de7141aa127d7debdbce1df39148dbec32
diff --git a/subcmds/download.py b/subcmds/download.py
index 0abe90d..6aa54af 100644
--- a/subcmds/download.py
+++ b/subcmds/download.py
@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import print_function
 import re
 import sys
 
@@ -68,23 +69,23 @@
     for project, change_id, ps_id in self._ParseChangeIds(args):
       dl = project.DownloadPatchSet(change_id, ps_id)
       if not dl:
-        print >>sys.stderr, \
-          '[%s] change %d/%d not found' \
-          % (project.name, change_id, ps_id)
+        print('[%s] change %d/%d not found'
+              % (project.name, change_id, ps_id),
+              file=sys.stderr)
         sys.exit(1)
 
       if not opt.revert and not dl.commits:
-        print >>sys.stderr, \
-          '[%s] change %d/%d has already been merged' \
-          % (project.name, change_id, ps_id)
+        print('[%s] change %d/%d has already been merged'
+              % (project.name, change_id, ps_id),
+              file=sys.stderr)
         continue
 
       if len(dl.commits) > 1:
-        print >>sys.stderr, \
-          '[%s] %d/%d depends on %d unmerged changes:' \
-          % (project.name, change_id, ps_id, len(dl.commits))
+        print('[%s] %d/%d depends on %d unmerged changes:' \
+              % (project.name, change_id, ps_id, len(dl.commits)),
+              file=sys.stderr)
         for c in dl.commits:
-          print >>sys.stderr, '  %s' % (c)
+          print('  %s' % (c), file=sys.stderr)
       if opt.cherrypick:
         project._CherryPick(dl.commit)
       elif opt.revert: