Allow apostrophes in email addresses when adding users via the Dashboard.

Email addresses entered in a number of interfaces were not being stripslashed
properly, with the result that the emails were not being recognized as valid.

Fixes #18039.

git-svn-id: https://develop.svn.wordpress.org/trunk@29966 602fd350-edb4-49c9-b593-d223f7449a82
Update expected results in wp_add_inline_style() unit tests after [29958].

props georgestephanis.
see #30032.

git-svn-id: https://develop.svn.wordpress.org/trunk@29967 602fd350-edb4-49c9-b593-d223f7449a82