Links from tutorial to std docs are broken

Example here:

http://static.rust-lang.org/doc/master/tutorial-tasks.html

Link for `std::comm` points to http://static.rust-lang.org/doc/master/std/comm.html where as the correct link would be http://static.rust-lang.org/doc/master/std/comm/index.html

This is relatively consistent error across the tutorials.
