Bring some sanity to request parsing and error handling (#2335)

* Update docs/request.md
* Bring some sanity to request parsing and error handling

- The browser can do JSON parsing itself. Let's defer to that where
  possible. (A few IE hacks are required here, though.)
- Don't propagate any error that occurs before `deserialize`/`extract`.
- Allow sending raw array buffers/blobs/etc. to `deserialize`.
- Align behavior more closely with the XHR spec.
- Send the more useful parsed response to `deserialize`, not the less
  useful string response.

request/tests/test-request.js

@@ -290,7 +290,7 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "GET", url: "/item", deserialize: deserialize}).then(function(data) {
-				o(data).equals("{\"test\":123}")
+				o(data).deepEquals({test: 123})
 			}).then(done)
 		})
 		o("deserialize parameter works in POST", function(done) {
@@ -304,12 +304,12 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "POST", url: "/item", deserialize: deserialize}).then(function(data) {
-				o(data).equals("{\"test\":123}")
+				o(data).deepEquals({test: 123})
 			}).then(done)
 		})
 		o("extract parameter works in GET", function(done) {
 			var extract = function() {
-				return JSON.stringify({test: 123})
+				return {test: 123}
 			}
 
 			mock.$defineRoutes({
@@ -318,12 +318,12 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "GET", url: "/item", extract: extract}).then(function(data) {
-				o(data).equals("{\"test\":123}")
+				o(data).deepEquals({test: 123})
 			}).then(done)
 		})
 		o("extract parameter works in POST", function(done) {
 			var extract = function() {
-				return JSON.stringify({test: 123})
+				return {test: 123}
 			}
 
 			mock.$defineRoutes({
@@ -332,7 +332,7 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "POST", url: "/item", extract: extract}).then(function(data) {
-				o(data).equals("{\"test\":123}")
+				o(data).deepEquals({test: 123})
 			}).then(done)
 		})
 		o("ignores deserialize if extract is defined", function(done) {
@@ -545,7 +545,8 @@ o.spec("xhr", function() {
 			})
 			xhr({method: "GET", url: "/item"}).catch(function(e) {
 				o(e instanceof Error).equals(true)
-				o(e.message).equals(JSON.stringify({error: "error"}))
+				o(e.message).equals("[object Object]")
+				o(e.response).deepEquals({error: "error"})
 				o(e.code).equals(500)
 			}).then(done)
 		})
@@ -568,7 +569,8 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "GET", url: "/item"}).catch(function(e) {
-				o(e.message).equals("Invalid JSON: error")
+				o(e.message).equals("null")
+				o(e.response).equals(null)
 			}).then(done)
 		})
 		o("triggers all branched catches upon rejection", function(done) {