Move the bytecode optimizer upstream so that its results are saved in pyc

Move the bytecode optimizer upstream so that its results are saved in pyc
files and not re-optimized upon import.  Saves a bit of startup time while
still remaining decoupled from the rest of the compiler.

As a side benefit, handcoded bytecode is not run through the optimizer
when new code objects are created.  Hopefully, a handcoder has already
created exactly what they want to have run.

(Idea suggested by Armin Rigo and Michael Hudson.  Initially avoided
 because of worries about compiler coupling; however, only the nexus
 point needed to be moved so there won't be a conflict when the AST
 branch is loaded.)