new edge-vector-branch

[bje at ozlabs dot au dot ibm dot com]

I have created a short-lived branch from mainline for the purposes of
completing my conversion of edge lists to edge vectors.  It uses the
new vec.h API and I've used the opportunity to do a number of
clean-ups where possible.  I've been bogged down for a couple of weeks
finding simple errors in my changes due to them manifesting themselves
in parts of GCC I'm not overly familiar with.

I've checked in the current state of my work and so if anyone would
like to help finalise this work, please feel free to send me patches.

Thanks, Ben