Continuing to map request headers using their name in uppercase for t…

…he index, but we now map to an object with an unmodified name and value: { name: "", value: "" }. This prevents overwriting of the user's supplied headers, which many applications parse with case sensitivity, because we no longer use the modified, uppercase index when building the request.

src/ajax.js

@@ -416,7 +416,7 @@ jQuery.extend({
 				// Caches the header
 				setRequestHeader: function( name, value ) {
 					if ( !state ) {
-						requestHeaders[ name.toLowerCase().replace( rucHeaders, rucHeadersFunc ) ] = value;
+						requestHeaders[ name.toUpperCase().replace( rucHeaders, rucHeadersFunc ) ] = { name: name, value: value};
 					}
 					return this;
 				},
@@ -664,24 +664,27 @@ jQuery.extend({
 
 		// Set the correct header, if data is being sent
 		if ( s.data && s.hasContent && s.contentType !== false || options.contentType ) {
-			requestHeaders[ "Content-Type" ] = s.contentType;
+			jqXHR.setRequestHeader( "Content-Type", s.contentType );
 		}
 
 		// Set the If-Modified-Since and/or If-None-Match header, if in ifModified mode.
 		if ( s.ifModified ) {
 			ifModifiedKey = ifModifiedKey || s.url;
 			if ( jQuery.lastModified[ ifModifiedKey ] ) {
-				requestHeaders[ "If-Modified-Since" ] = jQuery.lastModified[ ifModifiedKey ];
+				jqXHR.setRequestHeader( "If-Modified-Since", jQuery.lastModified[ ifModifiedKey ] );
 			}
 			if ( jQuery.etag[ ifModifiedKey ] ) {
-				requestHeaders[ "If-None-Match" ] = jQuery.etag[ ifModifiedKey ];
+				jqXHR.setRequestHeader( "If-None-Match", jQuery.etag[ ifModifiedKey ] );
 			}
 		}
 
 		// Set the Accepts header for the server, depending on the dataType
-		requestHeaders.Accept = s.dataTypes[ 0 ] && s.accepts[ s.dataTypes[0] ] ?
-			s.accepts[ s.dataTypes[0] ] + ( s.dataTypes[ 0 ] !== "*" ? ", */*; q=0.01" : "" ) :
-			s.accepts[ "*" ];
+                jqXHR.setRequestHeader(
+					"Accept",
+					s.dataTypes[ 0 ] && s.accepts[ s.dataTypes[0] ] ?
+						s.accepts[ s.dataTypes[0] ] + ( s.dataTypes[ 0 ] !== "*" ? ", */*; q=0.01" : "" ) :
+						s.accepts[ "*" ]
+					);
 
 		// Check for headers option
 		for ( i in s.headers ) {

src/ajax/xhr.js

@@ -104,7 +104,7 @@ if ( jQuery.support.ajax ) {
 					// Need an extra try/catch for cross domain requests in Firefox 3
 					try {
 						for ( i in headers ) {
-							xhr.setRequestHeader( i, headers[ i ] );
+							xhr.setRequestHeader( headers[ i ].name, headers[ i ].value );
 						}
 					} catch( _ ) {}