Sorry guys, this copying things from one side to the other is harder then I
thought, but I think I figured out how to do it ;)

Lop is based on the grad methods that are already implemented, while Rop
requires rop methods for each op that are going to be pushed soon.

Also now print for each apply if c code where used.

More cases are detected now.

zeros.

new optimization for dot products.

This flag is going to be used by optimizations. For example dot(zeros, X)
should be optimized out even if zeros is a constant.

Always update the following properties of current mode, even if current
function does not have profiling statistics: call_time, fn_time,
optimizer_time, linker_time. Re-add these attributes in ProfileMode
(they exist in Mode).

This basic timing functionality is used in particular for timing the deep
learning tutorials.

Also fix error that was causing compilation cache to fill up.