Jrobinson/configure for cross

The long awaited(?) pull request! I've tweaked things a bit so that commits that touch dist/, ext/, and cpan/ are at the "top" (the terminology escapes me), so you can merge just the important stuff and leave those out if it makes your life easier.
The very last commit touches Configure itself, so it definitely should not be merged. Also, I've left out the changes to make cross compilation work on a Mac host, because that's not quite working yet.