Update documentation with &share() non prototype checking version.

Update documentation with &share() non prototype checking version.
Fix share so it once again returns a reference to whatever it just
shared, so now you can do my &share([]);
Remove check for useithreads and Config.pm from threads::shared,
you can now always use threads::shared in your module without
overhead of config.pm and without speed hit unless threads have been
requested, share, cond_wait, cond_broadcast, cond_signal and lock
all become noops, so does : share.

p4raw-id: //depot/perl@17453