Fix _usergroup, cpio and chown completions

Improve test suite.
Thanks to Leonard Crestez (Alioth: #311396, Debian: #511788).

`assert_complete' is improved.  It proved difficult to tell tcl to ignore
backslash escapes, e.g. the `\b' is no BACKSPACE but a literal `b'.  The added
function `split_words_bash' should to the trick now.

Added function `assert_no_complete' which can also be reached by calling
`assert_complete' with an empty `expected' argument:

    assert_complete "" qwerty

1 files changed, 1 insertions, 0 deletions

diff --git a/CHANGES b/CHANGES
index dc626b1b..bb9f57d9 100644
--- a/CHANGES
+++ b/CHANGES
@@ -67,6 +67,7 @@ bash-completion (2.x)
   [ Leonard Crestez ]
   * Improve ssh -o suboption completion (Alioth: #312122).
   * Fix NFS mounts completion (Alioth: #312285).
+  * Fix completion of usernames (Alioth: #311396, Debian: #511788).
 
   [ Raphaël Droz ]
   * Add xsltproc completion (Alioth: #311843).