Ability to force a min/max range

Background
Currently the slider min/max is obtained from the facet data. The user interface it is a bit confusing because once you restrict the range, the min/max now adjusts to the range you just selected and is impossible to expand your selection.

Previously
This is an alternate approach to the same underlying issue in http://drupal.org/node/1239118 but it solves a slightly different problem. In that issue, the approach looked at was to obtain the global min/max value for a given query type.

Min/Max Irrespective of Data
In my situation, I want the slider to go from 1-5 even when there is no data with a value of 1.

This Patch
The approach here is to allow an user specified override of the min/max values used for the widget, irrespective of the actual facet data. There are a few questions around the behaviour that may need more consideration. Particularly, what if the user sets min to 10 and max blank, but the facet returns a min/max range of (2, 4). What should the max be then? Should we perhaps only allow min/max to be specified together? Currently in that situation, I leave min to 10 as specified, and clamp max to 10 also.

An alternate strategy I considered was to try to alter search results and override the min/max there but that seemed like the wrong place to do it as I think this is more a presentation layer (ie widget) issue.