Lightweight PDF reader with auto refresh
You can configure Skim to do this by executing 

defaults write -app Skim SKAutoReloadFileUpdate -boolean true

Which is a hidden preference:


  When this is true, and Skim checks for file updates on disk, the document is automatically reloaded without asking when there are no notes or edits. We don't recommend using this.


Note: Preferences → Sync → Check for file changes needs to be enabled if you haven’t already done so.

(I've tested this with Skim 1.4.8 and TL2013).