loadPlugins() should filter *.py files or given more obvious exception hint

when i debug installation for opensatck, i get a exception as follow:

[root@opencos127 home]# packstack --answer-file=/home/opencos_install/answers.txt
ERROR:root:Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/packstack/installer/run_setup.py", line 950, in main
    loadPlugins()
  File "/usr/lib/python2.7/site-packages/packstack/installer/run_setup.py", line 877, in loadPlugins
    fileList = sorted(fileList, cmp=plugin_compare)
  File "/usr/lib/python2.7/site-packages/packstack/installer/run_setup.py", line 863, in plugin_compare
    x_cmp = x_match.group(1)
AttributeError: 'NoneType' object has no attribute 'group'

ERROR : 'NoneType' object has no attribute 'group'
Traceback (most recent call last):
  File "/usr/bin/packstack", line 15, in <module>
    run_setup.main()
  File "/usr/lib/python2.7/site-packages/packstack/installer/run_setup.py", line 1020, in main
    print(output_messages.ERR_CHECK_LOG_FILE_FOR_MORE_INFO % (logFile))
UnboundLocalError: local variable 'logFile' referenced before assignment

the reason is there is a redundant file called .svn in /usr/lib/python2.7/site-packages/packstack/plugins/.