use WeakReference so that CGNode.getIR() doesn't hit the cache too often
Require that gen'd vector contains 0.  fixes #8
read runtime-visible annotations for fields
Merge pull request #15 from cos/cgnode-weakref-ir-defuse

use WeakReference so that CGNode.getIR() doesn't hit the cache too often
warning on SSAInstruction equals()
Merge pull request #16 from cos/warning-for-ssainstruction-identity

warning on SSAInstruction equals()
Merge commit '3c2a5f4ae4fb80f64f5049ef6efae74da6498223'