rename "chorder" to something more descriptive like "vote"

while working on http://drupal.org/node/51561, dries and i came to the conclusion that the db field name "chorder" (and the variables in the code that refer to it) is confusing and weird. ;) it should just be called something like "vote", which is what it is (the numeric offset for a given vote option on a given poll). or, if we want to be extra verbose in the name "vote_offset".

while we're at it, we should consider renaming "chvotes" in the {poll_choices} table to "total_votes". i guess "chtext" is ok, though maybe "vote_text" would be better? "chid" seems reasonable.

first step, get clear on exactly what we want to change, and what we want the new names to be.
then, someone can roll a patch for it.