use select instead of textfield for hostname filter

now a days I think it doesn't have any usability to set up the hostname search with any other option than contains

moreover NancyDru recommends to switch it to a select instead of a free textfield
and she made her point http://drupal.org/node/578488#comment-2125974

then this would be a support request which will wipe out the bug described above

PS: current bug doesn't affect users, since the default behavior is "contains", just the settings page offers 4 options that will be ignored: exact match, contains, starts with & ends with

hostname list will be limited due to log entries limit, but there might be several hostnames/IPs, since every access/login/logout from an external IP will create an entry

debate for having this as a select/textfield or even an autocomplete can be opened in another issue
but leaving here some bullets about it:
- having a select keeps uniformity between filters widgets
- since hostnames aren't showed at "Recent log" table there is no way to guess which one we might be interested on
- an auto-complete widget would have to be implemented from scratch, (username might use core's implementation, but this one does not exists)
- having a plain textfield would be pretty much unusable, since the administratios would have to guess what he/she is looking for (in this case I vote in favor of a "contains" operator and no other operator)

NOTE: this patch should remove file dblog_filters.host.admin.inc
no longer used after this patch

what about this one?