TempScop: Make assert more descriptive
Remove last uses of canoncial induction variable when scev code generating

We now detect scops without a canonical induction variable and can generate a
polyhedral representation for them. There was no modification necessary to
code generate these scops.
Do not canonicalize indvars with scev based codegen

Scev code generation can now handle scops with non canonical induction
variables. Hence there is no need to introduce canonical ones any more.
Add failing test case