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...
buffer: reject negative SlowBuffer offsets

Reject negative offsets in SlowBuffer::MakeFastBuffer(), it allows
the creation of buffers that point to arbitrary addresses.

Reported by Trevor Norris.
test: add cluster 'bind twice' test

This test starts two clustered HTTP servers on the same port.
It expects the first cluster to succeed and the second cluster
to fail with EADDRINUSE.

Reapplies commit cacd3ae, accidentally reverted in a2851b6.
Revert "tls: allow wildcards in common name"

This reverts commit 45024e7b7551eca7796e16fe453b2cbaee94b916.

It's making test/simple/test-tls-check-server-identity.js fail:

  AssertionError: Test#4 failed: { host: 'b.a.com',
    cert: { subject: { CN: '*.a.com' } },
    result: false }
      at <omitted>/test/simple/test-tls-check-server-identity.js:201:10
Revert "Revert "tls: allow wildcards in common name""

This reverts commit 30e237041d5cd7c39e33a9382c96f109be23337d.

Works properly with b4b750b
tls: follow RFC6125 more stricly

* Allow wildcards only in left-most part of hostname identifier.
* Do not match CN if altnames are present
dns: make error message match errno