* `before_populate_network`
* `after_populate_network`
* `after_upgrade_to_multisite`
These hooks are strategically located to allow the execution of custom code before & after a new multisite network is created, as well as after the first time a single-site installation is upgraded to multisite.
This change also includes a set of unit tests via a new `Tests_Multisite_PopulateNetworkHooks` class, to confirm that these hooks are executing when and as intended.
Props jeremyfelt, johnjamesjacoby, Mista-Flo, spacedmonkey, sukhendu2002, rmccue, rollybueno.
Fixes#27289.
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git-svn-id: http://core.svn.wordpress.org/trunk@60290 1a063a9b-81f0-0310-95a4-ce76da25c4cd