rcgroups urls for posts and threads

I haven't seen this documented anywhere, so I thought I would note it here.

an individual post (incidentally, the 17 millionth one!):

• http://www.rcgroups.com/forums/showpost.php?p=17000000

a post in the context of a thread:

• http://www.rcgroups.com/forums/showthread.php?t=1377399#post17252794

a thread, starting from the beginning:

• http://www.rcgroups.com/forums/showthread.php?t=1377399

first unread post in a thread:

• http://www.rcgroups.com/forums/showthread.php?t=1377399&goto=newpost