Fix drag-inline behavior with pholio stage background

Summary: Currently, if you click and drag in the checkered background, we'll create a 1px-wide or 1px-tall inline comment. Don't start inlines unless the user clicks on the image itself.

Test Plan: Clicked on and off the image.

Reviewers: chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D5227

webroot/rsrc/js/application/pholio/behavior-pholio-mock-view.js

@@ -194,7 +194,7 @@ JX.behavior('pholio-mock-view', function(config) {
 
   select_image(config.selectedID);
 
-  JX.Stratcom.listen('mousedown', 'mock-panel', function(e) {
+  JX.Stratcom.listen('mousedown', 'mock-viewport', function(e) {
     if (!e.isNormalMouseEvent()) {
       return;
     }