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/manifest.py b/subcmds/manifest.py
index 5592a37..5ceeb12 100644
--- a/subcmds/manifest.py
+++ b/subcmds/manifest.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 os
 import sys
 
@@ -69,7 +70,7 @@
                        peg_rev_upstream = opt.peg_rev_upstream)
     fd.close()
     if opt.output_file != '-':
-      print >>sys.stderr, 'Saved manifest to %s' % opt.output_file
+      print('Saved manifest to %s' % opt.output_file, file=sys.stderr)
 
   def Execute(self, opt, args):
     if args:
@@ -79,6 +80,6 @@
       self._Output(opt)
       return
 
-    print >>sys.stderr, 'error: no operation to perform'
-    print >>sys.stderr, 'error: see repo help manifest'
+    print('error: no operation to perform', file=sys.stderr)
+    print('error: see repo help manifest', file=sys.stderr)
     sys.exit(1)