Add support for Unix Domain Sockets to HTTP (client)

[mcavage]

As discussed out of band, I merged https://github.com/mcavage/node-httpu into core. Specifically I hacked up getAgent to take an options hash now, instead of host/port. It is entirely possible somebody overloading that is about to get broken. But presumably that list of people is ridiculously small, if it exists at all.

[mcavage]

Sorry - make test-all output:

bluesnoop:node mark$ make test-all
Waf: Entering directory /Users/mark/work/node/build' DEST_OS: darwin DEST_CPU: x64 Parallel Jobs: 1 Product type: program Waf: Leaving directory/Users/mark/work/node/build'
'build' finished successfully (0.096s)
python tools/test.py --mode=debug,release
Can't find shell executable: 'build/debug/node_g'
Can't find shell executable: 'build/debug/node_g'
Can't find shell executable: 'build/debug/node_g'
Can't find shell executable: 'build/debug/node_g'
=== release test-fs-chmod ===
Path: simple/test-fs-chmod
33279
assert.js:81
throw new assert.AssertionError({
^
AssertionError: 420 == 511
at /Users/mark/work/node/test/simple/test-fs-chmod.js:55:14
Command: build/default/node /Users/mark/work/node/test/simple/test-fs-chmod.js
=== release test-net-many-clients ===
Path: pummel/test-net-many-clients
cccccc
(node) Hit max file limit. Increase "ulimit -n"

node.js:181
throw e; // process.nextTick error, or 'error' event on first tick
^
AssertionError: 0 == 40960
at Socket. (/Users/mark/work/node/test/pummel/test-net-many-clients.js:77:12)
at Socket.emit (events.js:64:17)
at Array. (net.js:832:12)
at EventEmitter._tickCallback (node.js:173:26)
Command: build/default/node /Users/mark/work/node/test/pummel/test-net-many-clients.js

make: *** [test-all] Error 1