remove hard-coded value

In the future, this constant should disappear anyway.
don't check for exact buffer name

This is unnecessarily retrictive. check for compatible major mode instead.
fix issue 628

magit-log-author-date-overlay wasn't buffer-local
Merge branch 'issue-628'
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.