[OB PATCH] Fix some comments in thread.c

[OB PATCH] Fix some comments in thread.c

Fix some typos.
Remove obsolete comment about dispatch to thread_apply_command,
rather tell that thread_command either switches to a thread,
or prints the current thread.

2018-04-19  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* thread.c (thread_apply_all_command): Fix comment.
	(thread_command): Fix comment.