Use reraise and __STACKTRACE__ to reraise safe_insert_all errors

Fixes #1238

`reraise` is the current accepted idiom for reraising, not `raise` alone
as it preserves the original stacktrace.

apps/explorer/lib/explorer/repo.ex

@@ -57,7 +57,7 @@ defmodule Explorer.Repo do
             Logger.configure(truncate: old_truncate)
 
             # reraise to kill caller
-            raise exception
+            reraise exception, __STACKTRACE__
         end
 
       if returning do