proc: changed the way links to functions are fired: now Source/Proc instance is always passed as a parameter
proc: changed the way links to functions are fired: now Source/Proc instance is always passed as a parameter

- Source has a new property 'value' and a function exc_info() to access the result and the exception
- Source also has new functions has_value() and has_exception() to query the contents
- instead of p.link_value(lambda value: write('proc finished with result %r' % value) write
  p.link_value(lambda p: write('proc finished with result %r' % p.value)

tavisrudd/eventlet,tavisrudd/eventlet