Defer string evals of inlined accessors and constructors until first run.

If the class has been made immutable, fixup the stash.
Reduced the -e 'use Moose' startup time by 17%, on my machine anyway.
Tested accesses of inlined accessors without a noticeable effect on
efficiency. It just moves the eval'ing to runtime, so if your program
runs every accessor and constructor before causing a visible side
effect, it won't be any faster. The entire point of the fake RuNNeR
package is to fake out the inline_close_over test. If another way is
found to do that, then the bless isn't necessary. For example, we
could add a way to "run all the things", forcing them to string eval,
and the test could run that. Also, such a thing might be useful to
preforking servers, who would want to still eval everything before
forking.