Fix regression in `magit-refresh-wrapper' that caused status buffer to be refreshed twice.

This was introduced in 361f2d60: a manual conversion of `cl-adjoin'
missed a negation.
Merge pull request #635 from ncalexan/nalexander/refresh-regression

Fix regression that caused status buffer to be refreshed twice.
Merge remote-tracking branch 'origin/master'
Merge branch 'master' into next