made get and set headers case insensitive as per http1.1 spec

Author: daltonpearson

lib/browser/FetchHttpStack.ts

@@ -42,7 +42,7 @@ class FetchRequest implements HttpRequest {
   }
 
   getHeader(header: string) {
-    return this._headers[header]
+    return this._headers[header.toLowerCase()]
   }
 
   setProgressHandler(_progressHandler: HttpProgressHandler): void {
@@ -93,7 +93,7 @@ class FetchResponse implements HttpResponse {
   }
 
   getHeader(header: string): string | undefined {
-    return this._res.headers.get(header) || undefined
+    return this._res.headers.get(header.toLowerCase()) || undefined
   }
 
   getBody(): string {

lib/browser/XHRHttpStack.ts

@@ -42,12 +42,13 @@ class XHRRequest implements HttpRequest {
   }
 
   setHeader(header: string, value: string): void {
+    header = header.toLowerCase()
     this._xhr.setRequestHeader(header, value)
     this._headers[header] = value
   }
 
   getHeader(header: string): string {
-    return this._headers[header]
+    return this._headers[header.toLowerCase()]
   }
 
   setProgressHandler(progressHandler: HttpProgressHandler): void {
@@ -112,7 +113,7 @@ class XHRResponse implements HttpResponse {
   }
 
   getHeader(header: string): string | undefined {
-    return this._xhr.getResponseHeader(header) || undefined
+    return this._xhr.getResponseHeader(header.toLowerCase()) || undefined
   }
 
   getBody(): string {

lib/node/NodeHttpStack.ts

@@ -58,11 +58,11 @@ class Request implements HttpRequest {
   }
 
   setHeader(header: string, value: string) {
-    this._headers[header] = value
+    this._headers[header.toLowerCase()] = value
   }
 
   getHeader(header: string) {
-    return this._headers[header]
+    return this._headers[header.toLowerCase()]
   }
 
   setProgressHandler(progressHandler: HttpProgressHandler) {

test/spec/helpers/utils.js

@@ -96,11 +96,11 @@ export class TestRequest {
   }
 
   setHeader(header, value) {
-    this.requestHeaders[header] = value
+    this.requestHeaders[header.toLowerCase()] = value
   }
 
   getHeader(header) {
-    return this.requestHeaders[header] || null
+    return this.requestHeaders[header.toLowerCase()] || null
   }
 
   setProgressHandler(progressHandler) {
@@ -184,7 +184,7 @@ export class TestResponse {
   }
 
   getHeader(header) {
-    return this._response.responseHeaders[header]
+    return this._response.responseHeaders[header.toLowerCase()]
   }
 
   getBody() {