Merge branch 'ab/die-with-bug'

Code clean-up.

* ab/die-with-bug:
  object.c: use BUG(...) no die("BUG: ...") in lookup_object_by_type()
  pathspec: use BUG(...) not die("BUG:%s:%d....", <file>, <line>)
  strbuf.h: use BUG(...) not die("BUG: ...")
  pack-objects: use BUG(...) not die("BUG: ...")

builtin/pack-objects.c

@@ -3397,7 +3397,7 @@ static void read_object_list_from_stdin(void)
 			if (feof(stdin))
 				break;
 			if (!ferror(stdin))
-				die("BUG: fgets returned NULL, not EOF, not error!");
+				BUG("fgets returned NULL, not EOF, not error!");
 			if (errno != EINTR)
 				die_errno("fgets");
 			clearerr(stdin);