Broken link report doesn't handle redirects

[dontcallmedom]

see #201 #200 (websockets split-off) #186 #102 (html/C) #138 #87 (shortname change) #135 (w3c HTML to WHATWG, missing trailing /)

Not sure yet whether they should be handled by checking for an HTTP redirect happening, or through some other mapping mechanism (e.g. we currently maintain in-line a list of shortname changes)

[dontcallmedom]

see #201 #200 (websockets split-off)

dealt with by fixing them upstream rather than trying to make the script smarter

[dontcallmedom]

#138 #87 (shortname change)

Shortname change now properly reflected in the script