use findUniqueConcreteSubtype in InstanceOfNode
don't forget to record assumptions
ensure instanceof and null check stay dependent
Don't rewrite to trapping null checks if the FrameState has an input that's anchored to the deopting branch.

--HG--
extra : rebase_source : 15c8d773e37c5616118c3739a7ff0253a15c166f
Truffle: if value is null use instance stamps, not class or type stamps.
made Factory.newClassLoader() private
changed return type of Local.getType() to JavaType
added missing check for pending exception
added CHECK macros in uses of SymbolTable::new_symbol; added CHECK_ABORT macros for TRAPS functions that must abort the VM if they throw an exception