Switching function hashing to stay consistent across restarts

This could potentially pave the way for disk-caching of compiled graphs, etc.

Hello nicks, eford, 

Please review the following commits I made in branch 'azulus-compilerCache'.

d35341b00e99a60b20b5f1ae842db0e1e57a8967 (2013-05-20 10:19:53 -0700)
Flipped node hashing to stay consistent across multiple compiles

R=nicks
R=eford