Binary heap method to update an entry.

[Matthias Walter]

Hi all,

I uploaded [1] a patch for std.container to use BinaryHeap as a priority
queue. For the latter one it is often necessary to change a value (often
called decreaseKey in a MinHeap). For example, Dijkstra's shortest path
algorithm would need such a method. My implementation expects that the
user calls the "update" method after changing the entry in the
underlying store.

My method works for value-decrease and -increase, but one might want to
split this functionality into two methods for efficiency reasons. But I
thought it'll be better, because one can change the MaxHeap to be a
MaxHeap by changing the template alias parameter, but this wouldn't
change the method names :-)

The patch is against current svn trunk.

[1] http://xammy.xammy.homelinux.net/files/BinaryHeap-PriorityQueue.patch