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/abandon.py b/subcmds/abandon.py
index e17ab2b..b94ccdd 100644
--- a/subcmds/abandon.py
+++ b/subcmds/abandon.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 sys
 from command import Command
 from git_command import git
@@ -36,7 +37,7 @@
 
     nb = args[0]
     if not git.check_ref_format('heads/%s' % nb):
-      print >>sys.stderr, "error: '%s' is not a valid name" % nb
+      print("error: '%s' is not a valid name" % nb, file=sys.stderr)
       sys.exit(1)
 
     nb = args[0]
@@ -58,13 +59,13 @@
 
     if err:
       for p in err:
-        print >>sys.stderr,\
-          "error: %s/: cannot abandon %s" \
-          % (p.relpath, nb)
+        print("error: %s/: cannot abandon %s" % (p.relpath, nb),
+              file=sys.stderr)
       sys.exit(1)
     elif not success:
-      print >>sys.stderr, 'error: no project has branch %s' % nb
+      print('error: no project has branch %s' % nb, file=sys.stderr)
       sys.exit(1)
     else:
-      print >>sys.stderr, 'Abandoned in %d project(s):\n  %s' % (
-            len(success), '\n  '.join(p.relpath for p in success))
+      print('Abandoned in %d project(s):\n  %s'
+            % (len(success), '\n  '.join(p.relpath for p in success)),
+            file=sys.stderr)