Allow traversal up taxonomy hierarchy to parents instead of down to children

The attached patch, which is quite amateur, implements the ability to specify a negative depth as an option to the Taxonomy Term filter. This will result in the filter traversing up the tree to parents and grandparents, instead of down the tree to children and grandchildren.

It has some issues obvious to me while writing it, mostly due to my inexperience with drupal in general and the views api in particular.
The way I built the queries (a simple modification of the original to join children instead of parents) results in duplicate rows in the result. I can't see a reason not to use SELECT DISTINCT for views node searches in general, but that is outside the scope of this patch so I simply added a dumb GROUP BY to the query when using this filter. This can certainly be improved upon.
I duplicated the entire traversal loop in both the OR and AND portions of the filter. Having two nearly identical copies of the loop in the first place was wasteful of code size, my increasing it to four is even worse. Simplification may be in order here.

Since it already came up on IRC, I will mention that the use case here is for company memos at my place of business. We have a memos section, categorized by a company location heirarchy, with an Exposed filter for that category. We want users to be able to see memos for their location (usually an office) as well as parent locations (their city, state, and country, as 3 different levels above them). Without this patch the only solution we came up with was to use a multiple heirarchy built upside down, very hackish.