When creating an option via `add_option()`, the `$autoload` param allows you to
tell WP whether the option should be loaded as part of the 'alloptions' cache
during every pageload. `update_option()`, when used with a non-existent option
calls `add_option()` internally. The new `$autoload` param in `update_option()`
is passed along to `add_option()` in cases where the option does not yet exist.
The associated unit tests are skipped on multisite due to an issue that causes
`WP_INSTALLING` to force cache misses. See #31130.
Props codix, nofearinc, MikeHansenMe.
Fixes#26394.
git-svn-id: https://develop.svn.wordpress.org/trunk@31628 602fd350-edb4-49c9-b593-d223f7449a82
67324a9234