xdecref is a fair bit slower than decref (especially as it's implemented right
now as a helper function), but I think this will be ok once we get the llvm
jit up and running with refcounting.

First issue is that the assembly logging previously worked
on the assembler buffer, which is reasonable but has issues with the bjit
which will update the assembly post-relocation (ie by initializing the patchpoints).

Also add some extra flags to separate commenting for rewriter-level comments
("this is the beginning of a setattr") and the new bjit ones ("this is
a set local").

not sure about the code they emit though, since right now it's too large.

Current issue is that this is triggering the "mark IC as something
being inside", which trips up the bjit's "overwrite the last few
bytes of the previous block, assuming that they are just a jump".