[eigen] Blocks and EvalBeforeAssign

[Michael Tao <mtao@xxxxxxxxxxxxxxx>]

Hey all,
Currently assigning sub-blocks of variables to themselves like 
x = x.head(1);
returns garbage because Block doesn't have EvalBeforeAssigningBit set in
its Flags.  Is there a particular reason why EvalBeforeAssigningBit
isn't set in Block?

Here's a small full example where it breaks...
http://pastebin.com/3UYvYWwG
Though it usually outputs 0, sometimes it'll return something e-317,
which when casted as a double* is always approximately the value of
A.data().  Does anyone know why that might be happening?
Thanks,
Michael Tao