Moved to a separate function the code to emit a non-jittable optree.
Move start_op to the base Term class.

It's going to be used for all non-jittable trees, so it makes
sense to have it there.
Add helper function to get a B::Concise dump of the optree.
Avoid unintialized variable warnings on test failure.
Fix argument order in test function.
Fixed multiple layers of idiocy in jit_sub/jit_tree.

I particularly enjoyed the code that tested the subtrees member before
calling the method that populated it.
Traverse non-JITtable subtrees and JIT their JITtable subtrees.

Handles both non-handled opcodes/ast structures and subtrees for
which the user requested full Perl semantics.
$fun refactoring.

Having it as a member is not very clean, but we need it in all methods
and passing it explicitly is annoying.
Add some brain-dump-quality text on code generation.