Add support for profiling

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Wasted half an hour of already scarce hacking time to hunt where exactly a car 
gets a non-pair as argument. There is no stack in owl, but if primop errors 
would pass the registers, or at least the most common continuation register, to 
mcp, then the owl side could print something like a stack trace using the 
remaining chain of continuations.

To be useful, this would also need a way to associate a name to continuations 
generated from a named function. This would also useful for other debugging 
messages.

Original issue reported on code.google.com by aohelin on 10 Sep 2010 at 7:30