Set persp-add-on-switch-or-display to nil by default. Next time
switch/display-buffer advices will be removed. Small cosmetic changes.
Add custom option `persp-add-buffer-on-find-file';
Add `find-file-hook';
Fix `switchto-prev-buf-in-persp';
Small changes in: kill-buffer advice,`persp-add-buffer',
`persp-remove-buffer',`persp-temporarily-display-buffer'.