Add an end-to-end test for :history-clear

tests/end2end/features/history.feature

@@ -45,3 +45,8 @@ Feature: Page history
         And I wait for "Error while loading http://localhost:*/status/404: NOT FOUND" in the log
         Then the history file should contain:
             http://localhost:(port)/status/404 Error loading page: http://localhost:(port)/status/404
+
+    Scenario: Clearing history
+        When I open data/title.html
+        And I run :history-clear
+        Then the history file should be empty

tests/end2end/features/test_history_bdd.py

@@ -42,3 +42,8 @@ def check_history(quteproc, httpbin, expected):
             lines.append(line)
 
     assert lines == expected
+
+
+@bdd.then("the history file should be empty")
+def check_history_empty(quteproc, httpbin):
+    check_history(quteproc, httpbin, '')