Truffle: new infrastructure related to instrumentation, and in particular debugging: support for managing Source objects; framework for generalized "instrumentation proxy nodes" (to be inserted into ASTs with no runtime cost when inactive), and "probes" (which can be attached to proxy nodes to receive event notification); a rudimentary interface and abstract implementation for a "debug manager" (mostly a placeholder at this point); and the beginning of a language-agnostic ExecutionContext interface.