Remove one-time loop and redundant isset() checks in do_meta_boxes().

See [30022] for do_accordion_sections().

props ipm-frommen.
fixes #30093.

git-svn-id: https://develop.svn.wordpress.org/trunk@30040 602fd350-edb4-49c9-b593-d223f7449a82
When using 'show_in_menu' as a default value for 'show_in_admin_bar' in register_post_type(), cast to boolean instead of requiring a strict match.

props ipm-frommen.
fixes #30092.

git-svn-id: https://develop.svn.wordpress.org/trunk@30041 602fd350-edb4-49c9-b593-d223f7449a82