User search does not trim whitespace leading to good results not being returned

[tollmanz]

When searching for a user in a single site (in a network or single site install), addition of a leading or trailing whitespace can lead to no results being returned. While technically, the string with the whitespace isn't matched, the search string should be trimmed prior to the being used in the search.

To reproduce:
1) Go to wp-admin/users.php
2) Assuming you have a user with name "admin", search for "admin " (note the trailing whitespace)
3) No results will be returned (assuming no user with the "admin " exists)
4) Search for "admin"
5) The "admin" user account will be returned.

The search term should be trimmed before sending to WP_User_Query

Successfully tested against revision 21314.

Apache/2.2.21 (Win32) mod_ssl/2.2.21 OpenSSL/1.0.0e PHP/5.3.8 mod_perl/2.0.4 Perl/v5.10.1

Tested and can confirm it is working in version 3.5-alpha-21751

In [21864]:

Trim incoming searches on the users list table. props tollmanz. fixes #21318.