counsel-ag now works with ivy-occur-revert-buffer

counsel-ag now works with ivy-occur-revert-buffer

* ivy.el (ivy-occur-revert-buffer): Add `counsel-ag' to the list.

* counsel.el (counsel-ag-occur): Don't call `ivy-occur-grep-mode' unless
  needed.

> (string-match "\"\\(.*\\)\"" (buffer-name))

Is a hack to recover the old `ivy-text', since it's not a field in
`ivy-last', and may have changed in the meantime.

TODO: Fix this sort of hacks, all necessary session data should really be in `ivy-last'.