Organized imports

After an update to Mercurial 2.3 the module 'repo' was removed and the
program crashed when trying to convert a repository. I checked the
imports with 'pyflakes' and removed all unused ones, repo (among
others) was never used.

http://www.selenic.com/repo/hg/rev/1ac628cd7113#l9.1

hg-fast-export.py

@@ -3,10 +3,9 @@
 # Copyright (c) 2007, 2008 Rocco Rutte <pdmef@gmx.net> and others.
 # License: MIT <http://www.opensource.org/licenses/mit-license.php>
 
-from mercurial import repo,hg,cmdutil,util,ui,revlog,node
+from mercurial import node
 from hg2git import setup_repo,fixup_user,get_branch,get_changeset
 from hg2git import load_cache,save_cache,get_git_sha1,set_default_branch,set_origin_name
-from tempfile import mkstemp
 from optparse import OptionParser
 import re
 import sys