Shorten key used for browse happy site transient so it fits in option_name....

Shorten key used for browse happy site transient so it fits in option_name. fixes #17323, props AaronCampbell.

git-svn-id: https://core.svn.wordpress.org/trunk@17895 1a063a9b-81f0-0310-95a4-ce76da25c4cd