Add assert.
Re-evaluate regs should have a computation and a result.
Add assert.
Avoid invalidating computations that aren't in this context.
Reformat.
Replace condition with assert.
Make used_regs_for_reg( ) handle not having a computation.
Guard check for computation result.
Log a bit more MCMC stuff.
Print more edges in the debug graph.
Put back "call" edges to WHNF regs.
Use dlfcn-win32 on windows.
Handle empty initializer lists {}.

This is a workaround for LWG/EWG 2193, in which the default
constructor for vector<T> is explicit.

Also ensures compatibility with GCC 4.9.
Clang might begin to work.