[plt-scheme] Dr Scheme start position and size

I've also gone ahead and made drscheme remember the maximization state
(I had an old version of the docs and had forgotten that we have the
right support. Thanks for reminding me, Matthew!). As before, it only
maximizes the first window that it creates (and only if a maximize
happened (without any minimizes afterwards) the last time you ran
drscheme).

Turns out there is a bug in mac os x that Matthew is going to have to
work around before this'll work there, but it should be working now on
other platforms.

Robby