use replaceState if available, instead of setting the hash

www/code/main.js

@@ -495,9 +495,7 @@ define([
                 }
 
                 // set the hash
-                if (!readOnly) {
-                    window.location.hash = editHash;
-                }
+                if (!readOnly) { Cryptpad.setHash(editHash); }
 
                 Cryptpad.getPadTitle(function (err, title) {
                     if (err) {

www/common/cryptpad-common.js

@@ -225,6 +225,14 @@ define([
         return secret;
     };
 
+    var setHash = common.setHash = function (hash) {
+        if (!/^#/.test(hash)) { hash = '#' + hash; }
+        if (window.history && window.history.replaceState) {
+            return void window.history.replaceState({}, window.document.title, hash);
+        }
+        window.location.hash = hash;
+    };
+
     var storageKey = common.storageKey = 'CryptPad_RECENTPADS';
 
     /*

www/pad/main.js

@@ -601,9 +601,7 @@ define([
                 }
 
                 // set the hash
-                if (!readOnly) {
-                    window.location.hash = editHash;
-                }
+                if (!readOnly) { Cryptpad.setHash(editHash); }
 
                 Cryptpad.getPadTitle(function (err, title) {
                     if (err) {

www/poll/main.js

@@ -914,9 +914,7 @@ define([
                 editHash = Cryptpad.getEditHashFromKeys(info.channel, secret.keys);
             }
             // set the hash
-            if (!readOnly) {
-                window.location.hash = editHash;
-            }
+            if (!readOnly) { Cryptpad.setHash(editHash); }
 
             module.patchText = TextPatcher.create({
                 realtime: realtime,

www/slide/main.js

@@ -585,7 +585,7 @@ define([
 
                 // set the hash
                 if (!window.location.hash || window.location.hash === '#') {
-                    window.location.hash = editHash;
+                    Cryptpad.setHash(editHash);
                 }
 
                 Cryptpad.getPadTitle(function (err, title) {