caps issues:

 - We can't really tell until PAUSED that 'sinesrc ! identity ! ximagesink'
   will fail (since identity has ANY as the pad template caps).  
   Because of this, it's nearly useless to perform the pad
   template check.
   
   Alternatives:
     
     proxy pad template caps, but that reinstates the O(N^2) issue
     in 0.8 during linking lots of elements.

     remove checking of pad template caps compatibility

     add a means of checking a pipeline for caps compatibility before
     setting to PAUSED (ugly, requires special processing in each
     element)