Prompt about username change at sync time, not just in prefs

This is necessary because you can copy a database synced with a
different account into the data directory without affecting the stored
pref.

Also tweak the text to use proper quotes and remove quaint references to
"the server".

test/tests/syncLocalTest.js

@@ -21,6 +21,63 @@ describe("Zotero.Sync.Data.Local", function() {
 	})
 	
 	
+	describe("#checkUser()", function () {
+		it("should prompt for user update and perform on accept", function* () {
+			yield Zotero.Users.setCurrentUserID(1);
+			yield Zotero.Users.setCurrentUsername("A");
+			
+			waitForDialog(function (dialog) {
+				var text = dialog.document.documentElement.textContent;
+				var matches = text.match(/'[^']*'/g);
+				assert.equal(matches.length, 4);
+				assert.equal(matches[0], "'A'");
+				assert.equal(matches[1], "'B'");
+				assert.equal(matches[2], "'B'");
+				assert.equal(matches[3], "'A'");
+			});
+			var cont = yield Zotero.Sync.Data.Local.checkUser(win, 2, "B");
+			assert.isTrue(cont);
+			
+			assert.equal(Zotero.Users.getCurrentUserID(), 2);
+			assert.equal(Zotero.Users.getCurrentUsername(), "B");
+		})
+		
+		it("should prompt for user update and cancel", function* () {
+			yield Zotero.Users.setCurrentUserID(1);
+			yield Zotero.Users.setCurrentUsername("A");
+			
+			waitForDialog(false, 'cancel');
+			var cont = yield Zotero.Sync.Data.Local.checkUser(win, 2, "B");
+			assert.isFalse(cont);
+			
+			assert.equal(Zotero.Users.getCurrentUserID(), 1);
+			assert.equal(Zotero.Users.getCurrentUsername(), "A");
+		})
+		
+		it("should update local relations when syncing for the first time", function* () {
+			yield resetDB({
+				thisArg: this,
+				skipBundledFiles: true
+			});
+			
+			var item1 = yield createDataObject('item');
+			var item2 = yield createDataObject(
+				'item', { libraryID: Zotero.Libraries.publicationsLibraryID }
+			);
+			
+			yield item1.addLinkedItem(item2);
+			
+			var cont = yield Zotero.Sync.Data.Local.checkUser(win, 1, "A");
+			assert.isTrue(cont);
+			
+			var json = item1.toJSON();
+			var uri = json.relations[Zotero.Relations.linkedObjectPredicate][0];
+			assert.notInclude(uri, 'users/local');
+			assert.include(uri, 'users/1/publications');
+		})
+	});
+	
+	
 	describe("#getLatestCacheObjectVersions", function () {
 		before(function* () {
 			yield resetDB({