Fix logging error in sftp_client for filenames containing the character.

Bug reported here:
http://vlists.pepperfish.net/pipermail/obnam-flarn.net/2013-May/000767.html

Antoine Brenner

Backported to 1.11 by @bitprophet

Conflicts:
	paramiko/sftp_client.py
	sites/www/changelog.rst
	tests/test_sftp.py
Merge branch '1.11' into 1.12