darwin 64 bit support

[ianfasel]

To get 64-bit support, I was able to get a large chunk of 
boost-1_33_1 to build on darwin by inserting
   -arch ppc64
in strategic places in the darwin-tools.jam file. This was sufficient to 
be able to use the filesystem and program-options libraries in a 64-bit 
app I've built that needs to access > 4GB. Some libraries failed to 
build however, and I don't really know what I'm doing.

Attached is a patch file showing what I added where.  Also, it would 
probably be best to add
   -arch ppc -arch ppc64 
to get "fat" binaries that work for both 32-bit and 64-bit code.  
However I'm no pro with these things.