fix next/prev, small tweaks

pdf.js

@@ -1810,6 +1810,7 @@ var Page = (function() {
                                height: mediaBox[3] - mediaBox[1] });
             var args = [];
             var map = gfx.map;
+            contents.reset();   // TODO support multiple display()s
             var parser = new Parser(new Lexer(contents), false);
             var obj;
             while (!IsEOF(obj = parser.getObj())) {

test.html

@@ -44,6 +44,7 @@ function xhrstate() {
 }
 
 function displayPage(num) {
+    var start = Date.now();
     var page = pdf.getPage(pageNum = num);
     pageDisplay.value = num;
 
@@ -54,7 +55,6 @@ function displayPage(num) {
     ctx.restore();
 
     var gfx = new CanvasGraphics(ctx);
-    var start = Date.now();
     page.display(gfx);
     timeDisplay.innerHTML = (Date.now() - start) + "ms";
 }
@@ -77,7 +77,7 @@ function prevPage() {
   <div>
     <button onclick="prevPage();">Previous</button>
     <button onclick="nextPage();">Next</button>
-    <input type="text" id="pageNumber" value="0" size="5"></input>
+    <input type="text" id="pageNumber" value="1" size="5"></input>
     Time to render: <span id="time"></span>
   <div id="viewer">
     <!-- Canvas dimensions must be specified in CSS pixels.  CSS pixels