CodeGenKranc.m: Apply conversion from Mathematica to C repeatedly

Otherwise the divisions in the replacement rules might be converted into Power, which we want to remove.
Vectorisation.m: Use pow when dividing to avoid Power

Mathematica converts 1/y to Power[y,-1], and Power is not allowed in a C expression now.  Hence, write 1/y as pow(y,-1) for unvectorised code as this should be  optimised to divison by the compiler.
CodeGen.mt: Add withVectorisation wrapper
CodeGen.mt: Add and update tests for powers in vectorised expressions
Add check for Power in processed expression
Vectorisation.m: Allow Powers to accumulate during vector optimisation and convert them to pow afterwards
Vectorisation.m: Add commented-out debugging code
CodeGen.mt: Update tests
Update TestThorns submodule