[phobos] 64-bit

[David Simcha]

I saw Walter's latest checkin for DMD and needless to say, I'm extremely 
excited.  Is there an incomplete version of 64-bit DMD available yet 
that will do all frontend-related stuff assuming void*.sizeof == 8, 
size_t.sizeof == 8, etc. and then skip the codegen?  I would like to run 
it on the libraries that I use/develop (Phobos, dstats, parallelfuture) 
to have it check whether there are any issues related to improper 
assumptions about things like the size of pointers and size_t's and 
start fixing them now if there are any, so that when 64-bit support is 
complete these libs are ready to go.