/*
* call-seq:
* thr.group => thgrp or nil
*
* Returns the <code>ThreadGroup</code>whichcontains<i>thr</i>, or nil if
* the thread is not a member of any group.
*
* Thread.main.group #=> #<ThreadGroup:0x4029d914>
*/VALUErb_thread_group(thread)VALUEthread;{VALUEgroup=rb_thread_check(thread)->thgroup;if(!group){group=Qnil;}returngroup;}