Reset explore mode flag on pruning abandoned view

Otherwise it can be used after appropriate view_info structure has been
cleared.
Extract try_ressurect_abandoned() in view.c

Either makes use of abandoned view or prunes it.
Fix segfault on exploring same file in both views

Check for abandoned view didn't check target view.

Thanks to filterfalse.
Merge branch 'fix-segfault-on-viewing-same-file-in-two-panes'

Fix segmentation fault on exploring same file in both views.

Thanks to filterfalse.