There's a possibility I may need a binary heap in the near future,

and they're always handy things to have around. So here's a brand
new, but decently tested and apparently robust, generic binary heap
implementation just in case it comes in handy.

git-svn-id: svn://svn.tartarus.org/sgt/library@5065 cda61777-01e9-0310-a592-d414129be87e