Allow content negotiation when serving up a space.
Allow content negotiation when serving up a space.

This allows people in the know to send Accept headers to the
/ URI of a space to get other representations besides the wiki.
This is useful for testing, amongst other things.

TiddlySpace/tiddlyspace,FND/tiddlyspace,TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace,FND/tiddlyspace,FND/tiddlyspace