squid -- no sanity check of usernames in squid_ldap_auth

The LDAP authentication helper did not strip
leading or trailing spaces from the login name.
According to the squid patches page:

LDAP is very forgiving about spaces in search
filters and this could be abused to log in
using several variants of the login name,
possibly bypassing explicit access controls
or confusing accounting.
Workaround: Block logins with spaces

    acl login_with_spaces proxy_auth_regex [:space:]
	    http_access deny login_with_spaces