improving UI for issue query page's search "bar"

near the end of http://drupal.org/node/64648, dries suggested:

PS: can we wrap the search box in a fieldset so they look consistent with the 'Project information' fieldset, and the 'Issue information' fieldset on the 'new issue comment' page? :)

which he later clarified as:

The quick search bar on top of issue listings doesn't use a fieldset (example). I suggested (or tried suggesting ;)) that we make it use a fieldset as well (like the other "bars" in the project module).

basically, now that the create a new issue (or followup) form has the fieldsets that hold all the form elements horizontally (http://drupal.org/node/62129), we could attempt to do a similar thing on the issue query page, too, instead of the theme_ hook we're using now to stuff the form elements into a table (which used to be the state-of-the-art for this kind of thing).

while we're at it, we should probably use 2 bars of select elements (just like the other form), so you can query for whatever you want (what's there now, plus component, version, and possibly assigned). unfortunately, that gets tricky since the values to populate into the select box for component and version depend on what project is selected, so either we have to do some kind of active-select AJAX mojo to automatically alter the options whenever the project value is changed, or come up with a different plan...

if it's not going to have a good solution for adding version and component selectors, i'm not sure this UI change is worth the effort at the moment. just wanted to file a new issue to keep this work separate from #64648 (which was more limited in scope, and is now resolved).