Update name of a debian linux source package generated file.

tools/create_debian_packages.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 #
 
 # Script to build a Debian packages from a Dart tarball. The script
 # will build a source package and a 32-bit (i386) and 64-bit (amd64)
 # binary packages.
@@ skipping 83 matching lines @@
     if 'armel' in arch:
       print "Building armel package"
       RunBuildPackage(
           ['-B', '-aarmel', '-us', '-uc'], join(temp_dir, tarroot), toolchain)
 
     # Copy the Debian package files to the build directory.
     debbase = 'dart_%s' % version
     source_package = [
       '%s-1.dsc' % debbase,
       '%s.orig.tar.gz' % debbase,
-      '%s-1.debian.tar.gz' % debbase
+      '%s-1.debian.tar.xz' % debbase
     ]
     i386_package = [
       '%s-1_i386.deb' % debbase
     ]
     amd64_package = [
       '%s-1_amd64.deb' % debbase
     ]
     armhf_package = [
       '%s-1_armhf.deb' % debbase
     ]
@@ skipping 34 matching lines @@
 
   if not tar_filename:
     tar_filename = join(DART_DIR,
                         utils.GetBuildDir(HOST_OS),
                         'dart-%s.tar.gz' % utils.GetVersion())
 
   BuildDebianPackage(tar_filename, out_dir, arch, options.toolchain)
 
 if __name__ == '__main__':
   sys.exit(Main())