patch 7.4.1727

Problem:    Cannot detect a crash in tests when caused by garbagecollect().
Solution:   Add garbagecollect_for_testing().  Do not free a job if is still
            useful.

src/getchar.c

@@ -1523,7 +1523,7 @@ before_blocking(void)
     updatescript(0);
 #ifdef FEAT_EVAL
     if (may_garbage_collect)
-	garbage_collect();
+	garbage_collect(FALSE);
 #endif
 }
 
@@ -1571,7 +1571,7 @@ vgetc(void)
     /* Do garbage collection when garbagecollect() was called previously and
      * we are now at the toplevel. */
     if (may_garbage_collect && want_garbage_collect)
-	garbage_collect();
+	garbage_collect(FALSE);
 #endif
 
     /*