Add support for computational traces

[GoogleCodeExporter]

Want a capability similar to the current trace capability but want it to be a 
formal object that really tells exactly what happened (i.e. partial 
computations). This is to permit capabilities like the following:

1. Like in a theorem prover be able to walk back and reconstruct the proof.

2. All values to be changed at a particular point of a captured computational 
trace and then run from that point forward in order to be able to explore 
different possibilities.

Original issue reported on code.google.com by [email protected] on 11 Apr 2013 at 12:29