Add sudo_clobber and sudo_append functions so that we can "echo"

Add sudo_clobber and sudo_append functions so that we can "echo"
 and "cat" stuff and pipe it to something that can write to a 
file as root. For example:

echo "foo" | sudo_append /tmp/bar

will append "foo" to the file /tmp/bar as root. While

echo "foo" | sudo_clobber /tmp/bar

will truncate /tmp/bar and then write "foo" to the file.

[tedbo, 2010-04-12 17:28:28]

As you requested :-)

[Mandeep Singh Baines, 2010-04-12 17:49:34]

LGTM. Thanks!