fix bug where rotating the screen in a thread will take you back to the ...

...board page

For some reason screen rotation was causing the switchBoard method to be called in ThreadActivity, which starts a new BoardActivity.  I couldn't figure out why it is calling that but the simple fix is to check if the board you're switching to is already your current board, then no action is required.

There was also an issue when if you rotated the screen on a thread, then picked a new board, the board would not load.  I had to modify the if in BoardActivity in order for it to refresh properly, i'm not sure of the consequences of that.

I also removed some of the finish() calls, I don't know if they're necessary or not but it seems to work without it, and android will end up killing the activity right?