Release locks on abort

Fixes deadlock if hook_checkout returns ABORT.

One of these days I want to implement the abort mechanism through
exceptions, even though that means handling it explicitly in more
places. Or maybe *because* that means handling it explicitly in more
places.

lib/RevBank/FileIO.pm

@@ -60,6 +60,10 @@ sub release_lock() {
 	}
 }
 
+sub release_all_locks() {
+	release_lock while $lockcount;
+}
+
 sub with_lock :prototype(&) ($code) {
 	get_lock;
 	my @rv;