Change usages of xrange() to range()

In Python3, range() creates a generator rather than a list.

None of the parameters in the ranges changed looked large enough
to create an impact in memory in Python2.  Note: the only use of
range() was for iteration and did not need to be changed.

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

Change-Id: I50b665f9296ea160a5076c71f36a65f76e47029f
diff --git a/subcmds/stage.py b/subcmds/stage.py
index 2ec4806..1ff8588 100644
--- a/subcmds/stage.py
+++ b/subcmds/stage.py
@@ -58,7 +58,7 @@
       out.header('        %s', 'project')
       out.nl()
 
-      for i in xrange(0, len(all_projects)):
+      for i in range(len(all_projects)):
         p = all_projects[i]
         out.write('%3d:    %s', i + 1, p.relpath + '/')
         out.nl()