http: fix "Cannot call method 'emit' of null"

Fix the following exception:

  http.js:974
    this._httpMessage.emit('close');
                      ^
  TypeError: Cannot call method 'emit' of null
      at Socket.onServerResponseClose (http.js:974:21)
      at Socket.EventEmitter.emit (events.js:124:20)
      at net.js:421:10
      at process._tickCallback (node.js:386:13)
      at process._makeCallback (node.js:304:15)

Fixes #4586.
tls: allow wildcards in common name

see #4592
buffer: zero-length buffers shouldn't be slab-backed
install: add simplejson fallback

Make tools/install.py work with python 2.5

2.5 is still fairly widespread and does not include a json lib as
standard. Most python folk will have simplejson if they are in that
boat.

In general it seems a bit tricky to solve this perfectly...