Domain feature

This is a squashed commit of the main work done on the domains-wip branch.

The original commit messages are preserved for posterity:

* Implicitly add EventEmitters to active domain
* Implicitly add timers to active domain
* domain: add members, remove ctor cb
* Don't hijack bound callbacks for Domain error events
* Add dispose method
* Add domain.remove(ee) method
* A test of multiple domains in process at once
* Put the active domain on the process object
* Only intercept error arg if explicitly requested
* Typo
* Don't auto-add new domains to the current domain

    While an automatic parent/child relationship is sort of neat,
    and leads to some nice error-bubbling characteristics, it also
    results in keeping a reference to every EE and timer created,
    unless domains are explicitly disposed of.

* Explicitly adding one domain to another is still fine, of course.
* Don't allow circular domain->domain memberships
* Disposing of a domain removes it from its parent
* Domain disposal turns functions into no-ops
* More documentation of domains
* More thorough dispose() semantics
* An example using domains in an HTTP server
* Don't handle errors on a disposed domain
* Need to push, even if the same domain is entered multiple times
* Array.push is too slow for the EE Ctor
* lint domain
* domain: docs
* Also call abort and destroySoon to clean up event emitters
* domain: Wrap destroy methods in a try/catch
* Attach tick callbacks to active domain
* domain: Only implicitly bind timers, not explicitly
* domain: Don't fire timers when disposed.
* domain: Simplify naming so that MakeCallback works on Timers
* Add setInterval and nextTick to domain test
* domain: Make stack private

src/node.js

@@ -235,7 +235,13 @@
       nextTickQueue = [];
 
       try {
-        for (var i = 0; i < l; i++) q[i]();
+        for (var i = 0; i < l; i++) {
+          var tock = q[i];
+          var callback = tock.callback;
+          if (tock.domain) tock.domain.enter();
+          callback();
+          if (tock.domain) tock.domain.exit();
+        }
       }
       catch (e) {
         if (i + 1 < l) {
@@ -249,7 +255,9 @@
     };
 
     process.nextTick = function(callback) {
-      nextTickQueue.push(callback);
+      var tock = { callback: callback };
+      if (process.domain) tock.domain = process.domain;
+      nextTickQueue.push(tock);
       process._needTickCallback();
     };
   };